,a ,,guide ,,for ,,the ,,dissection     
,,of ,,the ,,dogfish                    
7,,squalus ,,acanthias7                 
,by                                     
,,lawrence ,e4 ,,griffin                
,professor of ,biology in ,reed ,college
                               ,,third  
,,edition                               
,portland1 ,oregon                      
#aibb                                   
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,copyright1 #aibb                       
by                           ,,lawrence 
,e4 ,,griffin                           
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,a ,guide for the ,dissection           
of the ,dogfish  ,the small sharks which
 abound along the coasts of the ,united 
,states are commonly called 8dogfish0 by
 fishermen and others4 ,the 8dogfish0 of
 inland waters belongs to an entirely   
different group4 ,two species of sharks 
are caught in numbers and used in       

laboratory work1 the 8spiny dogfish0    
7,squalus acanthias7 and the 8smooth    
dogfish0 7,eugaleus galeus74 ,the first 
is easily distinguished by the sharp    
spine in front of each dorsal fin4      
,squalus acanthias is often referred to 
under the synonym ,acanthias vulgaris1  
while ,eugaleus galeus is more          
frequently named either ,mustelus canis 
or ,galeus canis4 ,the histories of     
these names and systematic descriptions 
of the species are contained in ,samuel 
,garman's ,monograph on the             
,elasmobranchs4  ,several sizes of      
dogfish are furnished by dealers4 ,we   
consider it best to purchase large1     
fully developed specimens4 ,the small   
specimens may be a little more          
convenient to handle1 but the large ones
 have the important advantage of being  
sexually mature1 while blood vessels and
 nerves are dissected better in large   
than in small specimens4 ,also1 a number
 of structures are very different in    
mature animals from their condition in  

young ones4 ,dealers should be requested
 to furnish fish with fins and tails    
complete instead of trimmed4 ,it is an  
advantage to issue to the class equal   
numbers of both sexes4  ,an entire      
specimen and an extra head may be       
required by each student for a thorough 
dissection4 ,it would be better if the  
head were cut off just behind the       
pectoral fins1 instead of in front of   
them as is usually done1 so that the    
vagus and hypobranchial nerves may be   
dissected more completely4  ,the spiny  
dogfish1 which is the particular subject
 of this guide1 is the species most     
frequently supplied to laboratories4    
,however1 the spiny and smooth dogfishes
 are so much alike that the latter may  
be easily dissected with these          
directions4 ,where marked differences   
between the forms exist the structure of
 ,eugaleus is described separately4     
,the student of anatomy should realize  
that dissection is for the purpose of   
enabling him to see for himself the     

structures which exist1 and that no     
dissection is satisfactory until the    
anatomical arrangements mentioned in the
 text can be completely demonstrated in 
his specimen4  ,the importance of       
knowing the structure of the            
elasmobranch is so great in comparative 
anatomy and embryology that it is worth 
while to make a thorough dissection of  
one of this class4 ,as the dogfish is   
frequently the first major vertebrate   
form to be studied in detail1 these     
directions have been written to conform 
to the needs of the student who is      
beginning comparative anatomy4 ,the     
arrangement of sections in this guide is
 intended to permit the omission of some
 which it may not be considered         
desirable to include in the work of a   
class4                                  
,,external ,,characters  ,the           
spindle-shaped body tapers from near the
 middle toward both head and tail2 the  
head is flattened on both the dorsal and
 ventral sides1 while the remainder of  

the body is nearly round1 with a lateral
 compression which is not pronounced    
except in the caudal portion4  ,the     
general color of the back and sides is  
gray2 darkest above1 where the skin is  
spotted with scattered1 small1 round1   
light spots4 ,the color of the upper    
parts shades into the yellow white of   
the ventral surface4  ,can head1 trunk1 
and tail regions be distinguished8 ,if  
so1 what characters determine the extent
 of each8  ,a little above the middle of
 the side of the body is the lateral    
line1 7distinguished partly by color1   
partly by being slightly elevated71     
which extends from the back of the head 
to the tail4 ,cut through the skin      
across the lateral line at several      
points along the body and notice the    
canal which lies in the dermis under the
 lateral line4 ,this is the lateral line
 canal1 which opens to the surface by   
numerous pores 7too minute to be seen71 
and contains a series of special sense  
organs along its dorsal and inner       

surfaces4 ,near the base of the caudal  
fin the lateral line canal passes into a
 groove which continues the lateral line
 to within a short distance of the edge 
of the fin4 ,the lateral line canal in  
its development begins as a groove along
 the side of the body which becomes     
closed by the fusion of its edge except 
in this terminal portion4  ,the open    
groove does not appear in ,eugaleus4    
,in the midline of the body are two     
triangular dorsal fins1 each attached to
 the body for about half its length4    
,the basal portion of each is thick and 
muscular1 and contains supporting       
cartilages embedded in the muscles4 ,the
 remainder of the fin is flexible and   
semi-transparent1 horny fin-rays being  
faintly visible between the layers of   
skin4 ,in front of each fin is a strong 
spine which seems to serve both as a    
cutwater and a weapon of defense4       
7,eugaleus has no spines47  ,the broad1 
paired1 pectoral fins1 having the       
general characteristics of the dorsals1 

spring from the ventral edges of the    
body just back of the head4 ,a hard bar 
of cartilage connecting the bases of the
 pectoral fins can be felt through the  
skin of the ventral surface of the body4
 ,this is the ventral part of the       
pectoral girdle4  ,farther back1 and    
also on the ventral surface1 are the    
paired pelvic fins4 ,the pelvic girdle  
can be felt through the skin between the
 bases of these fins4 ,if the specimen  
is a male1 it will have a fingerlike    
process projecting backward from the    
base and along the inner side of each   
pelvic fin4 ,these organs1 which attain 
a considerable size in adults1 are      
modified portions of the pelvic fin used
 as copulatory organs4 ,they are named  
variously claspers1 myxopterygia1 or    
pterygopodia4 ,a groove runs along the  
dorsal side of the clasper from the tip 
to near the base1 where it opens into a 
long sac 7glandula pterygopodia7        
extending some distance in front of the 
pelvic fins just within the skin of the 

ventral surface4 ,by feeling a          
cartilaginous axis of the clasper can be
 discovered1 which extends to the tip of
 the organ4 ,on the dorsal surface and  
near the end of the clasper is a sharp  
grooved spine on the outer side1 and a  
strongly recurved hook on the inner     
side1 both almost hidden by a flap      
projecting from the inner edge of the   
groove4 ,this flap is stiffened by a    
series of small cartilages similar to   
the radial cartilages in the bases of   
the fins4  ,the caudal fin is           
asymmetrical1 extending along the dorsal
 and ventral edges of the posterior end 
of the body4 ,observe the upward bend of
 the vertebral column which occurs in   
the tail2 it is this character which    
marks the heterocercal type of tail4    
,eugaleus has a median ventral1 or anal1
 fin a short distance anterior to the   
caudal fin4  ,the mouth is a broad      
transverse slit upon the ventral surface
 of the head4 ,the cartilaginous jaws   
can be seen and felt just within the    

mouth4 ,both upper and lower jaws are   
armed with rows of flat1 sharply pointed
 teeth4 ,study their arrangement and    
approximate number4 ,jaws of previously 
dissected specimens should be examined  
under a dissection microscope4 ,the     
exact form and arrangement of the       
functional teeth can then be ascertained
 easily1 and an examination of the inner
 surface of either jaw will disclose    
several rows of developing teeth4 ,as   
the young teeth develop they move1 a row
 at a time1 into position on the edge of
 the jaw2 the oldest teeth1 occupying   
the outer row1 are shed at about the    
same time4  ,the upper jaw is partly    
overhung by a lip-like fold of skin4 ,at
 each side of the mouth is a pocket1    
directed obliquely1 having no           
communication with the mouth4 ,these    
labial pockets provide places for the   
labial cartilages 7which can be felt    
along the medial edges7 when the mouth  
is closed1 and also afford freedom of   
motion to the mandible4 ,cut along the  

inner edge of the labial pocket and     
expose the cartilages for examination4  
7,the labial pocket of ,eugaleus is much
 smaller1 and in front of the corner of 
the mouth rather than lateral to it4    
,the two cartilages are completely      
separated from each other1 the posterior
 one scarcely reaching the pocket47  ,in
 front of the mouth are the nostrils1   
their apertures apparently divided by   
projecting flaps of the anterior margin4
 ,explore the cavity of the nostril with
 a probe to get a good idea of its size 
and form4  ,between the pelvic fins is  
the cloaca1 a large depression into     
which open the alimentary canal1 the    
excretory and genital ducts1 and the    
abdominal pores4 ,the opening of the    
alimentary canal1 the anus1 is at the   
anterior end of the cloaca4 ,in         
preserved specimens part of the         
intestine is frequently everted through 
the anus4 ,a large fleshy process1      
bearing a pore at its tip1 projects from
 the dorsal wall of the cloaca4 ,in the 

male this is the uro-genital papilla2 in
 the female the urinary papilla4 ,in the
 female a genital pore1 the opening of  
the oviduct1 is found on either side of 
the papilla4 ,an abdominal pore1 leading
 into the abdominal cavity1 is found on 
each side of the cloaca at the posterior
 margin4 ,these are frequently closed in
 young specimens4  ,the cloaca of       
,eugaleus has a comparatively small     
opening upon the ventral surface1 which 
must be enlarged before the parts       
described can be seen well4  ,the       
laterally placed eyes are without lids2 
observe the considerable difference in  
the amount of curvature of the dorsal   
and ventral margins of the eye4  ,in    
,eugaleus there is a fold of skin       
stretched across the lower part of the  
eye which serves as an eye-lid1 and     
corresponds to the so-called 8third     
eye-lid0 or nictitating membrane of     
other vertebrates4  ,on each side of the
 neck are five vertical gill-clefts1    
each leading into a large gill pouch    

which communicates with the pharynx by  
an internal opening4 ,pass a probe      
through a gill-cleft into the mouth4    
,back of each eye is a small aperture1  
the spiracle2 explore this cavity with a
 probe4 ,the spiracle is to be          
considered a gill-cleft moved forward   
upon the head and largely1 though not   
entirely1 deprived of its respiratory   
functions4  ,in the center of the dorsal
 surface of the head1 between the       
spiracles1 are two pores1 the external  
openings of the endolymphatic ducts     
which communicate with the internal ear4
 ,large numbers of smaller pores can be 
found on all surfaces of the head1 some 
in groups1 some arranged linearly1 many 
scattered4 ,most of those arranged in   
lines lead into the sensory canal system
 which continues from the lateral line  
canal upon the head1 while the majority 
of the others belong to a separate type 
of sense organs1 the ampullae of        
,lorenzini4  ,make a cut encircling the 
pores of the endolymphatic ducts and    

close to them4 ,do not remove this piece
 of skin4 ,from it make a median        
incision forward to the tip of the snout
 and back as far as the level of the    
first gill slit4 ,starting at this      
incision work the skin off from the     
tissues beneath it4 ,this must be a     
careful1 close dissection4 ,when the    
lateral line is reached it will be seen 
that the lateral line canal is continued
 upon the head and is joined by several 
others4 ,by looking through the loosened
 skin toward the light the pores can be 
seen which lead from the canals to the  
surface4 ,in the hollow of the skull in 
front of and above the eye is a large   
group of tubules which open through the 
pores so conspicuous at this point4 ,at 
the internal end of each tubule is a    
slight enlargement1 of denser tissue1   
with which a delicate nerve strand can  
often be seen connected4 ,the nerve     
strands can be traced to a large nerve  
passing above the eye and distributed to
 the snout4 ,these tubules are the      

ampullae of ,lorenzini4 ,this group of  
ampullae1 which may be called the dorsal
 group1 is quite definitely demarked4   
,it will be noted that the inner ends of
 the ampullae are grouped in a much     
smaller area than their pores4  ,between
 the spiracle and the first gill slit   
will be found a lateral group of similar
 organs4 ,notice the arrangement of     
their tubules and pores4 ,under the     
snout are two groups of ampullae on each
 side of the midline4 ,the inner ventral
 group is separated from the outer      
ventral group by the lateral bar of the 
rostral cartilage4 ,some of the tubules 
of the outer ventral group will be found
 to extend to pores situated at the     
sides of and behind the mouth4  ,an     
adult fish possesses from #abjj to #aijj
 ampullae of ,lorenzini4 ,their function
 is not well understood1 but it has been
 suggested that they are organs         
responsive to stimuli of pressure1      
either of currents or water1 or         
resulting from depth1 or even of deep   

tones4  ,the system of sensory canals   
consists of the following members on    
each side of the head3--  ,a            
supra-orbital1 passing above the eye to 
the end of the snout and bending back on
 the ventral surface to join the        
infra-orbital4  ,an infra-orbital1 which
 branches off from the supra-orbital and
 passes ventrad between the eye and the 
spiracle1 then turns forward along the  
ventral margin of the orbit1 and finally
 bends toward the midline and extends to
 the tip of the snout4  ,a              
hyomandibular1 which leaves the         
infra-orbital below the eye and runs    
back beyond the angle of the mouth4  ,a 
short mandibular1 on the mandible close 
to the angle of the mouth1 which is not 
connected with the other canals4  ,the  
canal systems of the right and left     
sides are connected by a supratemporal  
canal just behind the endolymphatic     
pores1 and often by an anastomosis of   
the infra-orbital canals in front of the
 mouth4  ,on some specimens two         

crescentic rows of pores can be found   
between the bases of the pectoral fins1 
which represent a third type of sensory 
organ1 the pit organs1 closely related  
genetically to the sensory canals4 ,two 
longer lines of pit organs1 7the        
mandibular pit organs71 will be found a 
short distance behind the mouth4        
,similar pit organs are found in front  
of the endolymphatic pores1 and above   
the anterior part of the lateral line4  
,except for a few small areas the entire
 surface of the body is covered with    
small1 sharp-pointed denticles 7placoid 
scales74 ,each consists of a            
diamond-shaped basal plate embedded in  
the dermis1 from which projects a       
leaf-like1 backward directed spine4 ,a  
piece of skin should be removed and     
examined under a low magnification4 ,the
 dermis is so dense and pigmented that  
the basal plate is not easily studied   
without further manipulation4 ,for this 
purpose boil a piece of skin in #e      
caustic potash solution until it is     

softened1 but not till it disintegrates4
 ,then clear it in glycerine4 ,examine  
the individual denticles under a higher 
magnification4 ,the denticle consists of
 dentine1 the spine being of a much     
denser structure than the base4 ,the    
teeth and the large spines of the fins  
and claspers are also composed of       
dentine and may be considered as        
modified placoid scales4 ,denticles1    
teeth1 and spines are covered with a    
shiny1 enamel-like layer which1 however1
 does not appear to be true enamel such 
as covers the teeth of higher           
vertebrates4 ,the shape of the scales   
and their closeness vary on different   
regions of the body1 and there are      
certain regions entirely free from them1
 namely1 back of the dorsal1 pectoral   
and pelvic fins1 the medio-dorsal       
surfaces of the claspers1 inside the    
upper lip and the labial pockets4       
,,dissection ,,of ,,the ,,abdominal     
,,viscera  ,place the dogfish on its    
back and1 commencing at the middle of   

the abdomen1 make an incision through   
the body wall a quarter of an inch to   
one side of the midline4 ,carry this    
forward to the pectoral girdle and      
backward through the pelvic girdle to   
the cloaca2 not1 however1 cutting the   
wall of the cloaca4  ,a large vein1 the 
lateral vein1 runs along the inner      
surface of each lateral wall of the     
abdomen4 ,after identifying these1 cut  
through the body wall transversely on   
both sides of the abdomen at the level  
of the posterior attachment of the      
pectoral fin as far as the lateral vein4
 ,turn the flaps outward and fasten4    
,the coelom or body-cavity consists of  
two portions1 the abdominal and         
pericardial cavities4 ,the abdominal    
cavity1 which has now been opened1      
extends from the pectoral girdle to the 
cloaca and along the sides of the       
latter2 it communicates with the        
exterior through the abdominal pores on 
either side of the cloaca4 ,pass a      
bristle or probe through each abdominal 

pore into the cloaca4  ,without         
dissecting1 identify the following parts
 and observe their relations3  ,the     
peritoneum1 the smooth lining of the    
body wall1 which is reflected over the  
viscera4  ,the liver1 a large1 gray     
organ attached anteriorly and almost    
completely divided into two lobes which 
extend well back along the sides of the 
abdominal cavity4  ,the stomach1 lying  
between the lobes of the liver4 ,its    
posterior end is bent forward upon      
itself in the form of a ,u4 ,the two    
limbs of the stomach are known as the   
cardiac 7proximal7 and pyloric 7distal71
 respectively4 ,with a second turn to   
the right and backward it enters the    
intestine4  ,the intestine1 a large1    
thin-walled tube extending from the     
stomach to the cloaca4  ,the spleen1 a  
dark1 triangular mass attached to the   
posterior border of the curve of the    
stomach4  ,the spleen of ,eugaleus is a 
long1 slender body extending from the   
middle of the proximal limb of the      

stomach around the posterior end of that
 organ and forward again along the      
distal limb for two-thirds of the length
 of the latter4  ,the pancreas1 a firm  
white mass the larger part of which lies
 dorsal to the posterior end of the     
stomach4 ,one extremity lies on the     
ventral surface of the junction of the  
stomach and intestine4  ,the            
reproductive glands1 7ovaries or        
testes71 lying on either side of the    
midline dorsal to the anterior portion  
of the liver2 they may be mistaken for  
small lobes of the liver4  ,the         
reproductive glands of ,eugaleus are    
long bodies lying above the stomach and 
intestine4 ,they are fused to each other
 for almost their entire length4  ,the  
kidneys1 two long1 slender1 brownish    
bodies extending along the dorsal wall  
of the abdominal cavity outside the     
peritoneum1 on either side of the       
midline4  ,the dogfish usually furnished
 for dissection are immature1 having the
 genital glands and ducts only partly   

developed4 ,in mature females the       
oviducts are conspicuous tubes ventral  
to the kidneys4 ,in young specimens they
 appear as slender1 white tubes         
extending along the inner borders of the
 kidneys4 ,anteriorly1 the oviducts pass
 ventrad over the front of the liver to 
the ventral wall of the body2 at the    
same time they unite to form a funnel1  
the ostium tubae1 which opens into the  
coelom4 ,vestigial oviducts opening into
 the coelom are found in the same       
position in males4  ,in males1 the vasa 
deferentia appear as slender1           
irregularly coiled white tubules lying  
near the medial border of the kidneys2  
they are much less conspicuous than the 
oviducts1 especially in young males4    
,,the ,,alimentary ,,system4 ,in        
dissecting the following organs1 care   
should be taken not to break the        
connections of the organs with each     
other or with other parts1 or to cut    
blood vessels4 ,organs should not be    
removed until such procedure is         

directed4  ,the mouth and pharynx can be
 studied to better advantage later with 
the dissection of portions of the       
vascular system4  ,the oesophagus can be
 seen above the liver1 by pressing that 
organ aside1 as a somewhat constricted  
tube entering the anterior end of the   
abdominal cavity4 ,it immediately joins 
the stomach1 which is more or less      
expanded according to the amount of food
 contained in it4  ,the stomach passes  
directly back for more than half of the 
length of the abdominal cavity1 then    
turns abruptly forward1 forming a distal
 limb about a third as long as the      
proximal4 7,two-thirds to three-quarters
 as long in ,eugaleus47 ,the distal limb
 ends with a sharp turn to the right1   
where it is constricted by the pyloric  
sphincter1 which marks the end of the   
stomach4  ,the narrow beginning of the  
intestine forming the turn to the right 
and backward is frequently distinguished
 as the duodenum4 ,it leads from the    
stomach directly into the large         

intestine1 a wide1 straight tube marked 
externally by a spiral line of several  
turns4 ,the large intestine narrows     
posteriorly1 forming a region somewhat  
arbitrarily termed the rectum1 which    
opens into the cloaca through the anus4 
,dorsal to the rectum and attached to   
that body is a narrow spindle-shaped    
body1 the rectal or digitiform gland4   
,the liver is attached to the anterior  
wall by a broad base1 the peritoneum    
being reflected over the entire         
remaining surface4 ,the attaching fold  
of the peritoneum is frequently called  
the suspensory ligament4 ,the           
peritoneum1 or coelomic epithelium1 can 
be dissected easily from the surface of 
the liver or the kidney and its extreme 
thinness and delicacy noted4 ,it        
consists of a single layer of cells4    
,most of the abdominal organs are       
suspended from the dorsal wall of the   
body cavity by delicate membraneous     
sheets1 or mesenteries4 ,similar sheets 
between the organs are the omenta4 ,the 

stomach is suspended by a mesogaster1   
which extends as a free fold along the  
body as far as the anterior mesenteric  
and lienogastric arteries4 ,it encloses 
these1 and is attached to the spleen1   
pancreas1 stomach1 and anterior end of  
the intestine4  ,the spleen is connected
 with the stomach by the gastro-splenic 
omentum1 formed by an extension of the  
peritoneal coat of the stomach around   
the spleen4 ,the liver is connected to  
the loop of the stomach by the          
gastro-hepatic omentum in which are the 
hepatic duct1 portal vein1 and hepatic  
artery4 ,near the stomach it is joined  
by a fold of the peritoneum from the    
duodenum1 the duodeno-hepatic omentum1  
which also unites with the mesogaster4  
,the rectum and rectal gland are        
supported by a second median mesentery1 
the mesorectum4  ,in ,eugaleus the      
mesentery extends the entire length of  
the abdominal cavity4 ,it forms a broad 
sheet attached to the anterior end of   
the proximal limb of the stomach        

7mesogaster71 to the anterior end of the
 intestine 7mesentery proper71 and to   
the rectum 7mesorectum74 ,there is not  
the reduction of the mesentery which    
there is in ,squalus4 ,the gonads are   
suspended from the lateral faces of the 
mesentery above the stomach and         
intestine4 ,the gastro-hepatic omentum  
forms a broad sheet between the limbs of
 the stomach1 joining the mesogaster    
dorsal to the stomach and the mesentery 
above the intestine4  ,a small division 
of the right lobe of the liver stands   
out between the main lobes4 ,in this is 
located a long1 narrow gall-bladder4    
,open the bladder by a longitudinal     
ventral incision4 ,the opening into the 
bile duct will be found near the        
anterior end of the bladder4  ,in       
,eugaleus1 which does not possess such a
 median lobe1 the gall-bladder lies     
hidden in the right lobe of the liver4  
,it can be opened and explored1 but the 
connection with the duct can usually be 
demonstrated only by scraping4 ,do this 

later4  ,the bile duct passes along the 
dorsal side of the gall-bladder and the 
edge of the gastro-hepatic and          
duodeno-hepatic omenta to the junction  
of the duodenum and large intestine1    
where it opens into the alimentary      
canal4 ,trace its oblique course through
 the wall of the intestine4 ,the bile   
duct and the collecting 7hepatic7 ducts 
of the liver will be traced in the liver
 at a later stage of the dissection4    
,the pancreas consists of two lobes2 a  
slender lobe lying dorsal to and        
parallel with the stomach1 and a        
flattened oval lobe lying upon the      
ventral surface of the duodenum1        
connected with the dorsal lobe by a     
slender bar of glandular tissue4  ,the  
pancreatic duct passes from the extreme 
right end of the duodenal lobe obliquely
 through the wall of the intestine1     
opening into the anterior end of the    
large intestine4 ,free the edge of the  
lobe from the peritoneum and follow the 
duct4  ,open the proximal limb of the   

stomach by a ventral incision which     
shall not cut any large blood vessels4  
,wash out the interior4 ,observe the    
three coats of the stomach2 the outer   
peritoneal1 the middle muscular1 and the
 inner mucous coats4 ,in the anterior   
portion of the stomach the mucous coat  
projects in the form of large papillae  
7absent in ,eugaleus74 ,posterior to    
these1 observe the irregular folding of 
the mucous coat1 depending upon the     
degree of contraction of the muscular   
coat4  ,the muscular coat consists of an
 outer circular and an inner            
longitudinal layer of muscle fibres4    
,separate the two layers from each other
 and from the mucous coat2 observe the  
network of blood vessels between the    
longitudinal muscles and the mucosa4    
,open the pyloric end of the stomach1   
continuing the cut through the pylorus  
into the intestine4 ,examine the coats  
as before1 observing especially that an 
outer layer of longitudinal muscle      
fibres is frequently developed1 and that

 the pyloric valve is formed by an      
increase in the thickness of the coat of
 circular fibres4  ,cut through the wall
 of the large intestine along the right 
side from its anterior end to the       
rectum4 ,do not cut deeper than the     
thickness of the wall4 ,corresponding to
 the external markings1 the mucous      
membrane projects internally in a spiral
 fold1 known as the spiral valve4       
,separate the wall of the intestine from
 the edge of the spiral fold upon both  
sides of the longitudinal incision1     
exposing a considerable surface of the  
valve4 ,wash well1 and observe the      
character of the valve1 the direction of
 the folds1 and the manner of the       
reversal of their direction which       
usually takes place in the posterior    
half of the valve4  ,cut across the     
rectal gland at its middle4 ,observe the
 character of its tissues1 and then     
insert a bristle into the central cavity
 of the gland and pass it into the      
rectum4 ,open the rectum and note the   

point of communication of the two       
organs4  ,,urinary ,,and ,,reproductive 
,,organs4 ,the kidneys 7mesonephri1     
,wolffian bodies71 are slender bodies   
extending along the entire length of the
 dorsal wall of the abdomen4 ,the       
posterior moiety of each is thicker and 
wider than the anterior1 which appears  
to have largely lost the functions of   
excretion in adult dogfish4 ,notice the 
position of the kidneys outside the     
peritoneum4  ,,the ,,male4 ,the testes  
are white bodies lying to the right and 
left of the oesophagus1 dorsal to the   
anterior portion of the liver4 ,each is 
suspended by a fold of the peritoneum1  
the mesorchium4 7,the testes of ,galeus 
are long bodies attached to the sides of
 the mesentery47  ,showing through the  
peritoneum1 a much convoluted1 white    
tube can be seen on the ventral surface 
of the kidney4 ,this is the mesonephric 
or ,wolffian duct4 ,in young specimens  
it may be nearly straight1 lying near   
the medial border of the kidney4 ,in    

adult specimens it can be followed      
forward as far as the anterior end of   
the testis4 ,while the ,wolffian duct is
 the duct of the kidney1 and is joined  
by tubules of the anterior part of the  
kidney1 it is so modified in the male   
that its principal function is to serve 
as the duct of the testis1 a vas        
deferens4 ,the collecting tubules of the
 posterior part of the kidney join to   
form a urinary duct which is independent
 of the ,wolffian duct4 ,the posterior  
end of the ,wolffian duct is straight   
and considerably expanded1 forming a    
large seminal vesicle4 ,the duct becomes
 more and more closely convoluted as it 
passes forward1 and the kidney tissue   
overlying it diminishes4 ,at the        
anterior end of the mesonephros the     
,wolffian duct forms a mass of tubules1 
the epididymis4 ,very small tubules1 the
 vasa efferentia1 pass from the anterior
 end of the testis to the epididymis4   
,these are difficult for the student to 
distinguish4  ,cut through the          

peritoneum along the outer side of one  
kidney4 ,then strip the peritoneum      
toward the inner border of the kidney4  
,the urinary duct will usually be       
closely attached to the peritoneum and  
parallel with the ,wolffian duct1 but   
nearer the midline of the body4 ,the    
urinary duct can be separated from the  
peritoneum by a little careful work4    
,numerous small ducts pass from the     
kidney into the urinary duct4  ,open the
 uro-genital papilla near its tip and   
extend the incision forward so as to    
open the sac connected with the base of 
the papilla4 ,the pore at the tip of the
 papilla leads into a space within the  
papilla itself1 the uro-genital sinus1  
which branches to the left and right in 
pouches which extend beyond the         
posterior ends of the vasa deferentia4  
,these cornua of the uro-genital sinus  
are of variable length1 and are often   
named sperm-sacs4 ,in a mature male they
 may be found to be filled with sperm1  
as may also the seminal vesicles and the

 convoluted portion of the ,wolffian    
duct4 ,the openings of the vasa         
deferentia into the sinus are large and 
easily located4 ,the urinary duct opens 
into the sinus by a separate pore just  
behind the opening of the vas deferens4 
,cut open the seminal vesicle and part  
of the convoluted vas deferens4 ,the    
space within is subdivided by transverse
 folds or lamellae extending from a     
longitudinal ridge4  ,no vasa efferentia
 can be distinguished in ,eugaleus4 ,the
 anterior extremities of the kidney and 
testis of each side come into close     
contact with each other and here the    
vasa efferentia pass from the testis to 
the vas deferens4 ,the sperm-sac is a   
large blind pouch1 one or two inches in 
length1 leading out of the posterior end
 of the vas deferens1 and directed      
forward along its side4 ,the vas        
deferens of ,eugaleus is not convoluted4
  ,in the young specimens usually       
supplied to laboratories the vas        
deferens is straight and no seminal     

vesicle is developed4 ,the vasa         
efferentia are more difficult to see2   
otherwise the relations of the urinary  
and genital organs are as in the adult4 
,the suspensory ligament of the liver is
 continued posteriorly along the midline
 of the ventral body wall2 the dorsal   
edge supports a funnel which opens into 
the abdominal cavity by a long1 narrow  
mouth4 ,from the anterior end of the    
funnel two narrow tubes pass to the     
right and left over the anterior surface
 of the liver4 ,they end blindly in the 
tissues dorsal to the anterior end of   
the liver4 ,these are vestiges of the   
,muellerian ducts 7pronephric ducts7    
which form the oviducts of the females4 
,,the ,,female4 ,the ovaries are large1 
white bodies lying at the sides of the  
stomach1 dorsal to the lobes of the     
liver4 ,each is covered by the          
peritoneum and suspended by a fold of   
the same1 the mesovarium4 ,ova of       
various sizes may be felt in the tissue 
of the ovary1 which should be exposed by

 dissection4  ,the ovaries of ,eugaleus 
are long slender bodies lying on either 
side of the mesogaster1 dorsal to the   
stomach and intestine4 ,their posterior 
portions are fused4  ,the oviducts      
7,muellerian ducts7 are large tubes     
suspended from between the kidneys by a 
narrow peritoneal band4 ,the posterior  
portion of the oviduct1 where           
development of the eggs takes place1 is 
considerably enlarged4 ,each oviduct    
opens separately into the cloaca by a   
pore at the side of the urinary papilla4
 ,followed forward1 the oviducts pass   
over the anterior surface of the liver  
and following a continuation of the     
suspensory ligament1 bend around        
posteriorly and unite4 ,at the point of 
union they open into the coelom by a    
common1 large1 funnel-shaped aperture1  
the ostium tubae4  ,cut through the     
peritoneum along the outer side of one  
kidney4 ,then strip the peritoneum      
toward the inner side of the kidney4    
,numerous small excretory ducts will be 

seen joining the main urinary duct      
7,wolffian duct1 mesonephric duct71     
which runs along the inner margin of the
 kidney4 ,make an incision in the side  
of the urinary papilla to open the      
cavity within it1 the urinary sinus4    
,the connection of this with the pore at
 the tip of the papilla should be       
demonstrated4 ,extend the incision      
forward4 ,the urinary sinus divides into
 right and left cornua which are of     
considerable size and lie dorsal to the 
oviducts4 ,trace the ,wolffian duct to  
the urinary sinus and demonstrate its   
opening into the cornu anterior to the  
point where the two cornua unite4  ,in  
young specimens the ovaries are small1  
and the oviducts are narrow1 white tubes
 lying along the medial margins of the  
kidneys4  ,nephrostomes1 short1         
segmentally arranged kidney tubules     
which open to the coelom by a funicular 
aperture1 are found by a close          
examination along the medial border of  
each kidney4 ,they should be observed   

carefully with the aid of a good        
dissecting lens4 ,learn the significance
 of these structures4  ,in the course of
 development two sets of nephridia      
7kidneys7 are formed4 ,the first        
7pronephros7 develops just back of the  
head of the embryo1 but does not persist
 in the adult4 ,its duct1 known commonly
 as the ,muellerian duct1 develops into 
the functional oviduct of the female1   
but forms an apparently useless vestige 
in the male4 ,the second kidney         
7mesonephros7 develops behind the first 
and is the excretory organ of the adult4
 ,its duct 7frequently given the name of
 ,wolffian duct7 is the urinary duct in 
the female1 but functions in the male   
chiefly as a sperm duct1 and therefore  
is called the vas deferens4 ,the        
collecting tubules of the posterior     
portion of the kidney of the male unite 
to form a urinary duct which opens into 
the ,wolffian duct or the uro-genital   
sinus4                                  
,,respiratory ,,organs  ,open the       

anterior gill pouch of the left side by 
dorsal and ventral cuts extending from  
the angles of the cleft1 but cutting    
only as far as is necessary to see the  
structures within the pouch4 ,upon the  
medial side the gill pouch opens into   
the pharynx by a dorso-ventral slit1    
guarded by projecting cartilagineous    
gill rakers1 which prevent particles of 
food from passing into the gill pouch   
with the respiratory current4 ,on both  
the anterior and posterior wall of the  
pouch is a demibranch4 ,if the specimen 
is injected a large blood vessel can be 
seen through the skin in the inner      
border of the demibranch1 and small     
vessels passing from this into the      
leaflets1 where the interchange of gases
 between the water and blood takes      
place4  ,open similarly each pouch of   
the same side1 observing the number of  
the demibranchs and their relation to   
the pouches4  ,upon the anterior wall of
 the spiracle demonstrate a row of small
 vestigial gills2 being supplied with   

arterial instead of venous blood they   
form what is termed a pseudobranch4     
,,vascular ,,system  ,,heart ,,and      
,,ventral ,,aorta4 ,continue the        
longitudinal incision through the skin  
as far as the mandible4#a ,dissect away 
the sheet of muscles between the gill   
pouches and the mandible1 exposing a    
slender muscle which extends from the   
pectoral girdle to the middle of the    
mandible4 ,the thyroid gland lies dorsal
 to the anterior end of this muscle1    
close against the mandible4 7,the       
thyroid of ,eugaleus is a broad1        
flattened structure covering the        
anterior ends of the coracohyoideus     
muscles47 ,carefully dissect out the    
muscles lying between the branchial     
pouches of the right and left sides4    
,footnote #a3    ,see footnote1 p4 #ca4 
,in front of the pectoral girdle lies a 
thin-walled sac1 the pericardial sac4   
,open it by a median ventral incision4  
,remove about one-half inch of the      
middle of the pectoral girdle1 being    

careful not to cut the thin-walled part 
of the heart lying dorsal to it4 ,the   
pericardial cavity is a pear-shaped     
chamber containing the heart1 and lined 
by the smooth pericardium which is      
morphologically equivalent to the       
peritoneum4 ,at the anterior extremity  
of the chamber the pericardium is seen  
to be reflected backward over the       
surface of the heart1 thus forming its  
smooth outer coat4  ,the heart may be   
considered as a bent tube1 enlarged in  
certain regions to form the chambers4   
,anteriorly and ventrally is a short1   
thick-walled tube1 the conus arteriosus2
 this leads out of the pericardial sac  
anteriorly1 while posteriorly it opens  
into a large muscular chamber1 the      
ventricle4 ,dorsal to the ventricle1 and
 projecting on either side of it is the 
thin-walled auricle4 ,dorsal to both    
ventricle and auricle is the extremely  
thin-walled sinus venosus4 ,this is     
triangular in shape1 the apex opening   
into the posterior side of the auricle1 

the base attached to the posterior wall 
of the pericardial cavity2 the lateral  
angles are drawn out into the ducti     
cuvierii1 which receive veins from the  
anterior and posterior parts of the     
body4 ,from the conus arteriosus springs
 a smaller vessel1 the ventral aorta1   
which passes forward between the gill   
pouches4 ,take note of the small        
arteries passing over the surface of the
 conus and along the inner ends of the  
gill pouches1 and take care not to cut  
them or their branches in the subsequent
 dissection4  ,two pairs of arteries    
leave the ventral aorta as it emerges   
from the pericardial sac4 ,the aorta    
then passes forward some distance and   
finally divides into two branches which 
pass to either side4 ,follow the        
branches of the aorta outward on the    
left side and demonstrate their courses4
 ,the anterior branch quickly divides   
into two1 the anterior of these passing 
along the base of the first demibranch4 
,the posterior enters the septum between

 the first and second pouches1 and      
supplies the second and third           
demibranchs4 ,the middle branch of the  
aorta passes directly to the fourth and 
fifth demibranchs4 ,the posterior branch
 divides almost as it leaves the aorta1 
its branches supplying the remaining    
demibranchs4 ,there is considerable     
variation in this branch of the aorta4  
,it usually divides as stated1 but it   
frequently passes some distance toward  
the gills before dividing1 and in a     
considerable number of cases two vessels
 arise directly from the aorta instead  
of one4  ,the arteries carrying blood   
from the ventral aorta to the gills are 
named the afferent branchial arteries4  
,observe the relation of these vessels  
to the gills4  ,,venous ,,system4 ,all  
the blood of the body is conveyed to the
 sinus venosus4 ,the sides of the sinus 
venosus are extended as large vessels1  
already referred to as the ducti        
cuvierii4 ,open the sinus and ducti by a
 transverse ventral incision4 ,the ducti

 pass directly into the lateral veins4  
,near the middle of the posterior wall  
of the sinus is an aperture of varying  
size1 the opening of the hepatic sinus2 
there are rarely two openings in        
,squalus1 always two in ,eugaleus4 ,a   
large opening on the posterior wall of  
each ductus leads into the posterior    
cardinal vein4 ,on the anterior wall of 
the ductus1 near the sinus venosus1 is a
 small aperture1 that of the inferior   
jugular vein4 ,lateral to this is       
frequently a somewhat larger opening of 
the anterior cardinal vein4 ,this is    
absent1 however1 in the majority of     
specimens2 the anterior cardinals       
opening into the anterior ends of the   
posterior cardinals in about six out of 
ten cases4  ,a large cavity1 the hepatic
 sinus1 exists in the anterior end of   
the liver just posterior to the         
suspensory ligament4 ,cut into the liver
 at this point until the sinus is found1
 open it1 and observe the large hepatic 
veins bringing blood into it from the   

liver1 as well as its communication with
 the sinus venosus4  ,trace all veins by
 passing a flexible probe or guarded    
bristle along them and then opening the 
vein with the probe as a guide4 ,all    
smaller vessels emptying into those     
described should be noted4  ,the lateral
 veins pass forward to the posterior    
edge of the pectoral girdle1 bend       
sharply dorsad1 and enter the lateral   
extremities of the ducti cuvierii4 ,open
 a lateral vein near the anterior end   
and trace it toward the heart4 ,the     
right and left lateral veins are joined 
by a vein passing along the ventral bar 
of the pectoral girdle4 ,open the       
lateral veins at a point about two      
inches in front of the pelvic girdle and
 trace the veins backward as far as they
 can be followed4 ,the blood from the   
pelvic fins enters the lateral vein     
through the femoral vein4 ,the lateral  
veins finally unite back of the cloaca4 
,just before the lateral vein enters the
 ductus cuvierius it is joined by a     

large coracoid vein which runs dorsad   
and posteriorly along the posterior edge
 of the pectoral arch4 ,follow its      
course4 ,it receives a good-sized       
pectoral vein from the pectoral fin1 and
 sometimes several smaller veins from   
the same region4 ,traced dorsad it is   
found to open into a large blood sinus  
above the liver and oesophagus1 the     
cardinal sinus4  ,in ,eugaleus this     
connecting vein between the lateral vein
 and the cardinal sinus is wanting1 the 
pectoral vein opening directly into the 
lateral4  ,the ventral cutaneous vein1  
which runs along the ventral midline of 
the body wall1 should be followed2      
anteriorly it joins the vessel uniting  
the two laterals2 posteriorly it divides
 at the pelvic arch and anastomoses with
 the laterals4  ,pass a bristle from the
 sinus venosus into one of the posterior
 cardinal veins and trace the vein      
backward between the kidneys as far as  
possible4 ,open both posterior cardinals
 in this way1 washing them out and      

observing that they receive blood from  
the kidneys by a series of renal veins1 
and that they are separate in their     
posterior parts1 but communicate with   
each other anteriorly1 where they are   
greatly expanded2 the communicating     
portions and coincident enlargement     
forming the cardinal sinus4 ,the        
anterior portion of the cardinal vein   
receives ovarian or spermatic veins from
 the female or male gonad1 anterior     
oviducal veins from the anterior part of
 the oviduct1 and segmental veins from  
the corresponding region of the body    
wall4 ,there sometimes is more than a   
single opening from the posterior       
cardinal vein into the cuvierian duct4  
,cut across the tail an inch behind the 
cloaca4 ,two vessels lie in the         
cartilaginous arch below the centra of  
the vertebrae2 the dorsal of the two is 
the caudal artery1 the ventral one is   
the caudal vein4 ,follow the vein       
forward4 ,dorsal to the cloaca it       
divides into two1 which should be       

followed along the dorsal surfaces of   
the kidneys4 ,these are the renal portal
 veins1 conveying blood to the kidneys4 
,besides collecting the blood of the    
tail the renal portals also receive the 
posterior oviducal and segmental veins4 
,they pass into the capillaries of the  
kidneys4  ,the inferior jugular vein    
opens into the medial end of the        
cuvierian duct4 ,trace it forward along 
the ventral ends of the gill pouches2 it
 receives vessels from the arches and   
finally joins the hyoidean veins which  
follow the hyoid arch4 ,at the outer end
 of the cuvierian duct there is often a 
small opening on the anterior wall      
opposite the mouth of the posterior     
cardinal vein4 ,this leads into the     
anterior cardinal vein4 ,as mentioned   
before1 in a slight majority of the     
cases examined1 the anterior cardinal   
vein opens into the posterior cardinal  
vein1 not directly into the cuvierian   
duct4 ,if possible1 pass a bristle into 
the anterior cardinal4 ,to follow the   

vein1 and usually this is the best way  
to find it1 make a vertical longitudinal
 incision upon the dorsal side of the   
neck1 between the gill pouches and the  
mass of muscle lying beside the         
vertebral column4 ,this will open the   
anterior cardinal1 which is considerably
 expanded in this region1 and it may be 
traced from this point toward the heart 
and the head4 ,the anterior cardinal    
narrows suddenly in front of the        
anterior gill pouch1 and leads downward 
to the orbit1 where it expands into the 
orbital sinus surrounding the eyeball   
and its muscles4 ,trace the anterior    
cardinal only as far as the opening into
 the orbital sinus at this time4 ,veins 
from the anterior portion of the head   
and from the brain can be followed when 
the dissection of the eye is undertaken4
  ,just back of the spiracle the        
anterior cardinal receives the hyoidean 
vein1 which passes ventrad along the    
base of the first demibranch and unites 
with the hyoidean of the opposite side4 

,ventrally1 it also communicates with   
the inferior jugular vein4  ,the        
principal veins of the body have now    
been dissected with the exception of the
 hepatic portal vein1 which it is better
 to trace after the arteries of the     
digestive tract have been studied4      
,,the ,,efferent ,,branchial ,,arteries 
,,and ,,dorsal ,,aorta4 ,commencing at  
the mouth1 cut through the floor of the 
pharynx close to the left side of the   
ventral aorta and the heart4 ,the cut   
should leave the gill arches uninjured1 
and may be continued into the           
oesophagus4  ,examine the interior of   
the mouth and pharynx1 observing        
particularly the form and arrangement of
 the teeth1 the spiracular and branchial
 clefts1 the gill rakers1 and the       
character of the mucous coat of the     
pharynx4  ,remove the skin from the roof
 of the pharynx4 ,this exposes four     
pairs of efferent branchial arteries    
bringing blood from the gills and       
uniting in pairs to form the dorsal     

aorta4 ,follow each vessel of the left  
side out to its gill-cleft4 ,at the     
dorsal end of the gill-cleft it divides 
into a large posterior and small        
anterior branch4 ,these respectively    
pass along the posterior and anterior   
demibranchs of the gill pouch1 receiving
 fine branches from the gill lamellae1  
and finally unite again at the ventral  
end of the gill pouch4 ,thus a complete 
loop is formed around the branchial     
cleft4 ,the posterior branch of each    
efferent artery and the anterior branch 
of the succeeding one are united by     
several short vessels4 ,the efferent    
artery of the last demibranch possesses 
only these connections with the branch  
next anterior to it1 and none with the  
aorta directly4 ,from the ventral ends  
of the efferent loops small vessels pass
 toward the midline to unite with a     
longitudinal artery1 the hypobranchial  
artery1 which will be traced farther a  
little later in the dissection4  ,in    
,eugaleus the dorsal aorta extends      

forward beyond the union of the first   
pair of efferent branchials and then    
divides into small right and left       
branches which pass forward and outward 
to unite with the common carotid        
arteries4  ,a common carotid artery     
leaves the dorsal end of each anterior  
efferent branchial loop1 passing forward
 and inward4 ,at the level of the       
spiracles it divides into external and  
internal carotids2 the internal carotid 
unites with its fellow of the opposite  
side and enters the skull4 ,the external
 carotid arteries run outward and       
forward around the eyes and are         
distributed to the regions of the       
mandible and snout4 ,do not1 at present1
 trace them beyond the posterior edge of
 the eye4  ,another vessel arises from  
the middle of the anterior side of the  
first efferent branchial loop and runs  
forward to the spiracle1 where it ends  
in the capillaries of the pseudobranch4 
,this is the afferent hyoidean artery4  
,the term pseudobranch is used for the  

branchial lamellae of the spiracle      
rather than demibranch because of the   
arterial blood supply of this organ4    
,immediately after uniting the internal 
carotids divide and diverge1 forming an 
,x-shaped figure4 ,each anterior limb of
 the ,x again divides into two branches4
 ,the lateral branch passes to the      
ventral surface of the skull2 it        
presently gives off an anterior twig    
7ophthalmic artery7 which enters the    
eye4 ,it then passes on as the efferent 
hyoidean artery to the pseudobranch4    
,the inner of the two branchs mentioned 
above passes on as the internal carotid1
 sensu strictu1 and is distributed to   
the brain4  ,if the dissection is made  
with care1 the branches of the internal 
carotid can all be found without cutting
 any important nerves4 ,the branches    
passing to the eye and brain are best   
traced to their terminations in         
connection with the dissection of the   
nervous system4  ,near the union of the 
first pair of efferent branchial        

arteries a small posterior vertebral    
artery arises from each1 and runs       
anteriorly along the vertebral column4  
,near the divisions of the common       
carotids two anterior vertebral arteries
 arise from these vessels and pass      
posteriorly1 often anastomosing with the
 posterior vertebral arteries4 ,these   
vertebral arteries are vestiges of the  
former anterior part of the dorsal aorta
 7compare with ,eugaleus1 in which the  
dorsal aorta sends forward two vessels  
which join the common carotids74  ,an   
oesophageal artery springs from the     
second efferent branchial1 and passes   
back until it enters the wall of the    
oesophagus4 ,it also gives off nutrient 
branches to the second1 third1 and      
fourth gill pouches4 ,the nutrient      
artery of the first gill pouch arises   
directly from the first efferent        
branchial4  ,near the point at which the
 fourth pair of efferent branchials join
 the aorta1 two small subclavian        
arteries leave the aorta and pass into  

the pectoral fins4 ,there is some       
variation in regard to the point of     
origin of these vessels2 it may be      
either in front of or behind the        
junction of the fourth efferent         
branchials with the aorta4  ,the        
hypobranchial artery passes along the   
ventral ends of the gill pouches4 ,it is
 either connected with the efferent     
branchial loops by short branches1 or is
 formed1 in part at least1 by short     
vessels connecting these loops4 ,the    
hypobranchials are important nutrient   
vessels1 supplying the gill pouches and 
the muscles of the throat and the       
oesophagus by means of numerous small   
arteries2 from the hypobranchials also  
arise small posterior coronary arteries 
which pass to the ventral and posterior 
walls of the pericardium and the sinus  
venosus1 and larger anterior coronary   
arteries supplying the ventricle and    
conus arteriosus4 ,the hypobranchials   
can frequently he followed along the    
dorsal side of the pericardium and then 

outward to junctions with the subclavian
 arteries4  ,the coeliac artery 7coeliac
 axis7 arises from the aorta just back  
of the subclavians4 ,passing posteriorly
 and ventrad close to the right side of 
the stomach and reaching the            
gastro-hepatic omentum1 it divides into 
two branches1 the gastro-hepatic and    
anterior intestinal arteries4 ,the first
 gives off a small hepatic artery to the
 liver and a large gastric artery to the
 cardiac limb of the stomach4 ,the      
anterior intestinal artery supplies the 
pyloric limb of the stomach1 the        
pancreas1 duodenum1 and right side of   
the large intestine4  ,small genital    
arteries1 supplying the reproductive    
glands1 arise from the coeliac near its 
origin4 7,in ,eugaleus the genital      
arteries arise from the anterior and    
posterior mesenteric arteries47  ,at    
about the middle of the abdominal cavity
 two arteries arise close together from 
the aorta4 ,the anterior of the two is  
the anterior mesenteric artery2 it      

passes to the left side of the large    
intestine and its branches anastomose   
more or less with those of the anterior 
intestinal artery4 ,the posterior vessel
 is the lienogastric2 it goes to the    
spleen1 pancreas1 and loop of the       
stomach4  ,the posterior mesenteric     
artery leaves the aorta a little        
distance back of the lienogastric and   
passes to the rectal gland1 rectum1 and 
cloaca4  ,free the kidney from the body 
wall along its outer edge and turn it up
 so as to expose its dorsal surface4    
,observe the numerous parietal arteries 
7going to the body wall7 and renal      
arteries 7to the kidney71 which spring  
from the dorsal aorta4 ,branches of the 
parietals also pass into the kidney4  ,a
 pair of small iliac arteries pass into 
the pelvic fins4  ,oviducal arteries1   
one or several on each side1 arise from 
the aorta behind the coeliac artery and 
pass to the oviduct4 ,their size varies 
largely with the development and        
physiological condition of the oviduct4 

,the aorta is continued in the tail as  
the caudal artery4  ,,dissection ,,of   
,,the ,,heart4 ,remove the heart        
together with the ventral aorta from the
 body and fasten it1 dorsal side up1    
under water4 ,open the sinus venosus    
with scissors1 wash it out1 and observe 
the vertical slit-like opening into the 
auricle and the two membraneous valves  
which guard it4  ,continue the cut      
through the sinu-auricular aperture     
along the median dorsal line of the     
auricle2 observe the thin walls of the  
auricle and their strengthening by an   
irregular mesh of muscles1 the musculi  
pectinati2 the shape and position of the
 auriculo-ventricular aperture2 the     
flaps of the auriculo-ventricular valve4
 ,press upon the sides of the ventricle 
and1 if possible1 observe the mode of   
action of the valve4  ,cut across the   
ventricle from the auriculo-ventricular 
aperture4 ,carry another incision from  
this along the dorsal side of the conus 
arteriosus4 ,observe the small size of  

the cavity of the ventricle1 the        
thickness of its walls1 and the         
projecting network of muscles1 the      
columnae carneae1 some of which are     
attached to the edges of the            
auriculo-ventricular valves4  ,in the   
conus arteriosus observe the rows of    
three pocket-like valves each around the
 proximal end 7semilunar valves71 and a 
single row of three similar but larger  
valves at the junction of the conus and 
ventral aorta4 ,there is some           
variability in the number of rows of    
valves in the conus of ,squalus2 there  
are always three rows of three valves   
each in that of ,eugaleus4  ,in the     
aorta notice the apertures without      
valves which lead into the afferent     
branchial vessels4  ,,hepatic ,,portal  
,,system4 ,the hepatic portal vein is   
the large vein entering the liver       
alongside the hepatic artery and bile   
duct4 ,it receives branches from the    
stomach1 pancreas1 spleen1 intestine1   
and rectal gland4  ,at the surface of   

the liver it divides into two branches1 
which enter the two lobes of this organ4
 ,within the liver the hepatic portal   
veins branch until a capillary system is
 formed from which the blood is         
collected by the hepatic veins and      
carried into the sinus venosus4  ,in    
general1 the branches of origin of the  
hepatic portal vein follow closely the  
arteries of the digestive organs4 ,trace
 the following parts of the system3 ,a  
posterior intestinal vein1 from the     
rectal gland and rectum1 the large      
intestine and spiral valve1 across to   
the end of the pancreas1 along the      
pancreas to the hepatic portal vein2 an 
anterior intestinal vein1 from the large
 intestine and spiral valve1 along the  
duodenal lobe of the pancreas2 gastric1 
duodenal1 and pyloric veins joining the 
veins already traced2 a splenic vein    
joining the posterior intestinal vein4  
,the liver1 with the bile duct1 may now 
be removed from the body if it is       
desired to trace the bile duct into the 

bladder or to trace the hepatic ducts4  
,this can be done best by gently        
scraping away the soft liver tissue     
until the bladder and ducts are exposed4
                             ,,the      
,,nervous ,,system4  ,only the head and 
anterior part of the trunk will be      
required for the dissection of the      
nervous system4 ,cut across the body    
back of the pectoral fins2 the posterior
 part of the body will not be required  
further unless it is desired to study   
the muscles and skeleton4  ,the manner  
of dissecting the brain depends somewhat
 upon the specimens at the disposal of  
the student4 ,if a large head is to be  
used especially for the dissection of   
the cranial nerves1 only the brain1 eye 
and ear need be studied in the present  
specimen4 ,but in most cases it will be 
found best for the student to dissect   
the first dogfish as thoroughly as      
possible1 working out the cranial nerves
 as well as the brain1 and reserving the
 second head for a thorough review of   

the entire nervous system4 ,chapter     
,,iii of ,herrick and ,crosby's         
8,laboratory ,outline of ,neurology0    
should be used in connection with such a
 review4  ,if a line be drawn over the  
dorsal surface of the head connecting   
the two spiracles1 two small pores will 
be found near the middle4 ,these are the
 external apertures of the ducti        
lymphatici4 ,cut carefully through the  
skin in a small circle around the pores1
 and remove the skin from the remainder 
of the dorsal surface of the skull      
without disturbing the small section    
containing the pores4 ,the latter part  
should now be lifted gently2 beneath it 
will be seen two delicate tubes passing 
from the pores to apertures in a        
depression of the skull below them4     
,these tubes are the ducti              
endolymphatici1 through which a passage 
exists between the internal ear and the 
exterior4 ,as they cannot be preserved  
in the subsequent dissection1 the pores 
by which they pass through the skull to 

the internal ear should be found now1   
and a memorandum-sketch made of the     
ducts themselves4  ,,dorsal ,,surface   
,,of ,,the ,,brain4 ,the roof of the    
skull should be removed from over the   
brain4 ,use a sharp scalpel and take    
very thin slices of cartilage4 ,do not  
cut beyond the brain at the sides4 ,no  
attempt should be made at this time to  
expose more than the dorsal surface of  
the brain4  ,above the anterior end of  
the brain there is a small median       
foramen through the skull1 the          
epiphysial foramen4 ,a strand of tissue1
 the epiphysis1 leading from this to the
 surface of the brain1 should be        
carefully observed and retained4 ,the   
cartilage should also be cut away from  
above the portion of the spinal cord    
next the skull4 ,gently wash away any   
coagulated lymph4  ,the brain and spinal
 cord are invested by two membranes     
7meninges74 ,the tough dura mater lines 
the cavity in which they lie1 clinging  
closely to the cartilage2 in fact it    

forms the perichondrium of the internal 
surface of the cranium4 ,the pia mater  
envelops closely the brain and cord1 and
 contains numerous blood vessels4       
,between the two is the arachnoid space1
 traversed by occasional fine threads of
 connective tissue and filled with      
lymph4  ,as the spinal cord passes      
forward into the skull it enlarges and  
merges with the posterior portion of the
 brain1 the medulla oblongata           
7myelencephalon74 ,the roof of the      
medulla is extremely thin1 and is broken
 if the cartilage has not been removed  
with extreme care1 exposing a cavity    
within1 the fourth ventricle4  ,in front
 of the medulla1 and overlapping its    
anterior extremity1 is a large oval     
organ1 the cerebellum 7metencephalon74  
,ventral to the cerebellum1 each side of
 the medulla is expanded in an          
ear-shaped lobe1 the corpus restiformis4
 ,anteriorly1 the cerebellum overlaps a 
pair of rounded lobes1 the optic lobes1 
which together form the dorsal portion  

of the midbrain 7mesencephalon74  ,in   
front of the optic lobes are two        
slightly larger lobes united in their   
posterior portions but separated        
anteriorly1 the cerebral lobes or       
hemispheres4 ,together they constitute  
the prosencephalon4 7,the prosencephalon
 is not divided in ,eugaleus47 ,between 
the mesencephalon and the prosencephalon
 is a depressed region belonging to the 
brain-stem1 the diencephalon            
7thalamencephalon71 from which the      
epiphysis arises4 ,the roof of the      
diencephalon also is very thin and is   
frequently broken during the exposure of
 the brain4 ,the cavity seen within the 
diencephalon is the third ventricle4    
,stalked bodies arising from the        
antero-lateral angles of the cerebral   
hemispheres are the olfactory lobes4    
,the portion of the brain including the 
cerebral hemispheres and the olfactory  
lobes constitutes the telencephalon4    
,,dissection ,,of ,,the ,,internal      
,,ear4 ,the structures composing this   

organ lie in the projecting cartilage at
 the side of the medulla 7auditory      
capsule74 ,remove the cartilage of the  
auditory capsule in thin slices and bit 
by bit1 following the ductus            
endolymphaticus to the membraneous      
labyrinth4 ,dissect away the surrounding
 cartilage leaving the membraneous      
canals in place1 until the entire       
labyrinth is exposed4 ,the membraneous  
labyrinth consists of a large central   
sac 7utriculo-saccular chamber7 into    
which the endolymphatic duct opens1 and 
three membraneous tubes 7semicircular   
canals7 external to the chamber but     
communicating with it in various ways4  
,two1 one anterior and the other        
posterior to the sacculus1 lie in a     
nearly vertical plane 7anterior and     
posterior semicircular canals72 one is  
external to the sacculus and lies in a  
nearly horizontal plane 7horizontal or  
external semicircular canal74 ,at the   
ventral ends of the vertical canals are 
nearly spherical enlargements called    

ampullae4 ,the ampulla of the horizontal
 canal is at its anterior end4 ,the     
dorsal ends of the vertical canals open 
near each other into the upper part of  
the utriculo-sacculus4 ,the ventral     
extremity of the anterior vertical canal
 and the anterior extremity of the      
horizontal canal open beside each other 
into an anterior projection of the      
sacculus4 ,the ventral extremity of the 
posterior vertical canal opens into the 
posterior and lower part of the         
sacculus4 ,the posterior extremity of   
the horizontal canal opens into the     
posterior side of the sacculus4 ,during 
life the utriculo-sacculus and the      
semicircular canals are filled with a   
lymphatic fluid1 and the sacculus       
contains a large calcareous ear-stone   
7otolith71 which is usually dissolved by
 the formalin used in preserving the    
dogfish4  ,whitish patches of thickened 
sensory epithelium may be seen in the   
ampullae 7cristate acusticae7 and in the
 utriculo-saccular chamber 7maculae     

acusticae74 ,branches of the eighth     
nerve can be followed to all these      
areas4  ,a projection of the ventral    
wall of the utriculo-sacculus is the    
lagena1 the rudiment from which the     
cochlea of higher animals developed4 ,it
 also contains a macula acustica4       
,,external ,,features ,,of ,,the ,,eye4 
,observe the transparent cornea covering
 the external surface of the eye2 the   
dark ring of the iris2 the central      
opening in the iris1 the pupil2 the     
conjunctival sac surrounding the        
external half of the eyeball4 ,cut away 
sufficient of the upper wall of the     
cartilaginous orbit to expose the       
eyeball and its muscles4 ,note the      
considerable amount of soft connective  
tissue around the eye and explore the   
orbital sinus 7p4 #ac74 ,take notice of 
the following nerves1 in order to ensure
 their preservation until the time comes
 to trace them more completely4 ,a large
 nerve crossing the medial side of the  
orbit1 the superficial ophthalmic2 a    

nerve leaving the cranium opposite the  
optic lobe1 passing under the           
superficial ophthalmic to the anterior  
muscle of the eyeball1 the trochlear2   
several long ciliary nerves passing to  
the eyeball2 several other nerves       
visible in the deep angle of the orbit4 
,six muscles move the eye4 ,four of     
these arise close together at the deep  
postero-medial angle of the orbit4      
,diverging1 they are inserted upon four 
sides of the eyeball1 and from the      
position of their insertions are named  
the superior1 posterior1 inferior1 and  
anterior recti4 ,two muscles arise from 
the antero-medial angle of the orbit1   
the superior and inferior oblique       
muscles4  ,between the recti muscles can
 be seen a mushroom-shaped stalk of     
cartilage1 the ophthalmic peduncle2 the 
eyeball rests against its expanded end4 
7,there is no peduncle in ,eugaleus47   
,,the ,,cranial ,,nerves4 ,the cranial  
nerves are twelve pairs of nerves       
arising from the brain1 and thus        

distinguished from the spinal nerves    
which arise from the sides of the spinal
 cord4 ,they are distributed chiefly to 
the head and neck1 though branches of   
the vagus nerve go to the viscera and to
 the sense organs of the lateral line4  
,since the nerves are all paired1 the   
distribution of both nerves of a pair   
being alike1 the descriptions will      
mention but one nerve of a pair4 ,as the
 cranial nerves are traced dissect away 
the sides of the cranium down to the    
foramina penetrated by the nerves1 and  
follow each nerve from its origin on the
 brain to the parts innervated by it4   
,features of the dissection which are   
not found in tracing the nerve of one   
side should be sought on the other side4
  ,the olfactory nerve4 ,the anterior   
surface of the olfactory lobe fills a   
large foramen in the anterior wall of   
the cranium and is pressed closely      
against the posterior surface of the    
nasal sac4 ,numerous small nerves1      
collectively forming the olfactory      

nerve1 arise from the anterior face of  
the lobe1 penetrate the membraneous wall
 of the olfactory organ1 and are        
distributed to its highly folded        
surface4  ,the terminal nerve1 ,nervus  
terminalis1 is a slender nerve running  
along the medial surface of the stalk of
 the olfactory lobe4 ,follow it backward
 to its origin on the anterior surface  
of the cerebral hemisphere1 deep in the 
median fissure 7in ,eugaleus on the     
ventral surface74 ,trace it forward over
 the dorsal surface of the olfactory    
lobe to where it enters the nasal sac4  
,the terminal nerve is a true cranial   
nerve which has escaped notice until    
recent years4 ,it is associated with the
 olfactory nerve in vertebrates         
generally from fishes to men4 ,the      
fibres of the terminal nerve remain     
distinct from those of the olfactory    
nerve1 both in the olfactory organ and  
in the brain4 ,its function is unknown4 
,there is still a division of opinion   
among authorities as to whether the     

terminal nerve should be considered to  
be a distinct cranial nerve1 or a       
portion of the olfactory nerve4  ,the   
optic nerve can be seen at the bottom of
 the orbit between the eye and the      
skull1 nearly under the superior oblique
 muscle4 ,it arises from the ventral    
side of the diencephalon1 passes        
outward1 penetrates the orbit at its    
infero-medial angle1 and continues      
directly outward to the eyeball4  ,the  
trochlear nerve1 or patheticus1         
penetrates the wall of the orbit        
opposite the optic lobe4 ,follow it back
 to its origin from the dorsal surface  
of the brain in the depression between  
the optic lobes and the cerebellum4     
,then follow it from the skull to the   
superior oblique muscle1 which it       
innervates4  ,the oculo-motor nerve     
arises from the ventral surface of the  
midbrain1 passes outward1 and penetrates
 the orbit on a level with and just     
anterior to the origins of the recti    
muscles4 ,it divides immediately into   

three parts2 two pass to the anterior   
and superior recti respectively1 while  
the third passes downward along the     
posterior surface of the eyeball to the 
inferior rectus and inferior oblique    
muscles4 ,in tracing this nerve the     
palatine process of the upper jaw will  
be seen projecting from below into the  
orbit4  ,the trigeminal1 facial1 and    
auditory nerves spring from the side of 
the medulla below the corpus            
restiformis4 ,the roots1 and some of the
 branches1 of the trigeminal and facial 
nerves are so mingled as to be          
indistinguishable except by special     
neurological technique4 ,the common root
 of the trigeminal and facial nerves    
shows a partial division into a dorsal  
and a ventral portion2 the dorsal       
portion belongs to the facial nerve1    
while the ventral root is mixed4 ,the   
root of the auditory nerve lies close   
behind the trigeminal-facial root1 but  
can be distinguished fairly well4 ,both 
the trigeminal and facial nerves divide 

into several trunks1 namely3            
,trigeminal      ,facial                
superficial     superficial             
ophthalmic      ophthalmic              
deep ophthalmic buccal                  
maxillary       otic                    
mandibular      hyomandibular  ,the     
superficial ophthalmic trunks of the two
 unite in a single nerve which passes   
along the inner wall of the orbit above 
the muscles of the eye to a foramen in  
the antero-medial angle of the orbit1   
through which it passes to the dorsal   
surface of the snout4 ,the superficial  
ophthalmic nerve of ,squalus is composed
 almost entirely of fibres of the facial
 nerve4 ,the superficial ophthalmic     
trunk of the trigeminal gives rise to   
several small nerves leaving the common 
trunk near its origin and passing to the
 skin above the eye4 ,the superficial   
ophthalmic trunk of the facial1 nearly  
the whole of the common nerve1 branches 
profusely to supply the sensory organs  
of the dorsal and lateral surfaces of   

the snout4  ,the superficial ophthalmic 
of ,eugaleus rises from the dorsal part 
of the trigemino-facial root and leaves 
the cranium by a separate foramen above 
and anterior to the roots of the recti  
muscles4  ,directly under the origin of 
the superficial ophthalmic will be found
 a comparatively slender nerve1 which   
passes between the superior and         
posterior rectus muscles1 and forward   
along the medial surface of the eyeball2
 it penetrates the anterior wall of the 
orbit by a separate foramen1 and emerges
 under the superficial ophthalmic4 ,it  
is distributed to the skin of the dorsal
 and lateral surfaces of the snout4     
,this is the deep ophthalmic            
7ophthalmicus profundus7 of the         
trigeminal nerve4 ,a slender branch     
7posterior ciliary nerve7 passes from   
the deep ophthalmic near its origin to  
the posterior surface of the eyeball4   
,farther forward the same trunk gives   
off an anterior ciliary nerve to the    
anterior part of the eyeball4  ,a large 

nerve which crosses the floor of the    
orbit1 beneath the eyeball1 consists of 
the maxillary trunk of the trigeminal   
and the buccal trunk of the facial      
nerve4 ,these remain associated1 even   
into the small branches4 ,near the      
anterior margin of the orbit the        
maxillary-buccal trunk divides into     
three parts2 the smallest and outer one 
passes to the surface lateral and       
anterior to the eye4 ,the other two dip 
downward and pass in front of the jaw to
 the ventral surface of the snout4      
,reflect the skin of the ventral surface
 of the snout1 and by dissection expose 
these nerves as they emerge from the    
orbit4 ,the larger branch runs forward  
close to the median line of the snout1  
giving off numerous twigs2 the other1   
which appears to be a pure trigeminal   
branch1 is distributed near the angle of
 the mouth4 ,the fibres of the maxillary
 trunk supply the skin1 while those of  
the buccal go to the canal organs and   
ampullae of ,lorenzini4  ,the mandibular

 trunk of the trigeminal nerve arises   
beneath and behind the maxillary4 ,it   
passes outward in front of the levator  
maxillae superioris muscle1 sending a   
few twigs into this muscle1 and turns   
downward over the palato-quadrate       
cartilage4 ,it divides here1 one part   
entering the adductor mandibularis      
muscle1 the other passing downward along
 the edge of the mandible1 innervating  
the skin of the lower jaw and the first 
ventral superficial constrictor muscle4 
,the mandibular and maxillary-buccal    
trunks of ,eugaleus are united until    
they approach the edge of the orbit1 and
 the palatine branch is much larger2    
otherwise the trigemino-facial branches 
are much as in ,squalus4  ,the          
hyomandibular trunk of the facial nerve 
can be found just beneath the skin      
behind and close to the spiracle4 ,from 
here it can be followed back to the     
brain4 ,it arises from the ventral part 
of the trigemino-facial root1 emerging  
from the cranium through the            

hyomandibular canal4 ,it divides into a 
number of branches just beyond the      
spiracle3  #a4 ,the external mandibular 
branch consists of two portions1 a small
 anterior nerve extending               
antero-ventrally to the canals above and
 below the angle of the mouth1 and a    
larger nerve which passes laterally and 
suddenly breaks up into a brush of twigs
 which innervate the hyoidean group of  
ampullae4  #b4 ,the internal mandibular 
branch arises at about the same level as
 the external mandibular1 but under it1 
passes inward around the edge of the    
hyoid cartilage1 under the adductor     
mandibularis muscle1 and then forward   
along the mandibular cartilage4  #c4    
,the hyoid branch separates from the    
hyomandibular trunk at about the same   
level as the preceding nerves1 and then 
passes1 deep in the tissues1 around the 
angle of the jaw to the ventral side    
where it is distributed to the          
superficial constrictor muscles4        
,several nerves pass from the           

hyomandibular trunk and the hyoid branch
 to the dorsal superficial constrictors4
  #d4 ,the palatine branch springs from 
the base of the hyomandibular trunk     
inside the hyomandibular canal4 ,it     
passes outward and forward1 dividing    
into numerous branches which innervate  
the mucous membranes of the mouth4 ,it  
can be traced completely later4  ,one or
 more small nerves proceeding to the    
pseudobranch and anterior wall of the   
spiracle arise near the point of origin 
of the palatine branch4  ,the otic      
nerve1 passing from the root of the     
facial nerve to the postorbital canal1  
is not likely to be found in this       
dissection4  ,observe the enlargement   
near the base of the hyomandibular      
trunk1 and within the cartilaginous     
canal1 the geniculate ganglion4 ,the    
gasserian ganglion1 a component of the  
trigeminal nerve1 lies in the ventral   
portion of the trigeminal-facial root1  
and can now be located4  ,the auditory  
nerve arises close behind the ventral   

division of the trigemino-facial root4  
,the root of the auditory nerve encloses
 a large auditory ganglion4 ,a          
vestibular nerve arises from the        
anterior end of the auditory ganglion   
and passes into the ear capsule1        
innervating the upper part of the       
utriculo-sacculus and the ampullae of   
the anterior and horizontal canals4     
,from the posterior part of the ganglion
 nerves pass to the ventral part of the 
sacculus and the ampulla of the         
posterior canal4 ,trace these branches  
as thoroughly as possible4  ,the        
abducens nerve emerges from the cranium 
under and close to the origin of the    
posterior rectus muscle1 into which     
muscle it enters4 ,to expose this nerve 
the trigeminal1 facial and auditory     
nerves must be lifted and cut as they   
pass through the wall of the cranium4   
,it can be traced obliquely backward and
 inward1 through a long canal1 to its   
origin near the midline of the ventral  
surface of the medulla4  ,the           

glossopharyngeal nerve passes through   
the base of the ear capsule from the    
side of the medulla to the upper end of 
the first branchial pouch4 ,a ganglionic
 enlargement is found near where it     
emerges from the cartilage4 ,outside the
 cranium the glossopharyngeal divides   
into a pretrematic branch1 passing down 
in front of the first gill pouch1 and a 
posttrematic branch running behind the  
pouch4 ,the pretrematic branch quickly  
sends off a pharyngeal nerve which runs 
antero-ventrally to the roof of the     
pharynx4 ,the pretrematic and           
posttrematic branches can be followed   
along the gill arch to the ventral side 
of the pharynx4 ,a fourth branch of the 
glossopharyngeal1 the supratemporal1    
springs from the dorsal side of the     
ganglion2 passing through the ear       
capsule it runs to the dorsal surface of
 the head1 where it is distributed to   
the sense organs of a short section of  
the lateral line canal4 ,this small     
nerve can be demonstrated by carefully  

separating the muscles and perichondrium
 from the posterior surface of the      
auditory capsule4  ,the vagus nerve 7or 
pneumogastric7 arises by an extensive   
series of roots from the side of the    
medulla4 ,an easily distinguished       
ribbon-like portion of the root1 the    
lateral line root1 runs forward as far  
as the root of the glossopharyngeal4    
,note the canal by which the vagus      
leaves the cranium1 and trace the nerve 
along the inner side of the anterior    
cardinal vein4  ,the principal branches 
of the vagus are3  #a4 ,the             
supratemporal branch1 a small nerve     
running dorsal through the posterior    
part of the ear capsule to the lateral  
line canal and other sense organs of the
 head4 ,it will be found near the       
supratemporal branch of the             
glossopharyngeal4  #b4 ,the lateral line
 branch1 a large nerve which separates  
from the trunk of the vagus just outside
 the cranium and runs backward through  
the muscles1 parallel to the vertebral  

column on a level with the lateral line4
 ,it sends off numerous small twigs to  
the sense organs of the lateral line    
canal4  #c4 ,four branchial nerves1     
which can be seen through the floor of  
the anterior cardinal vein1 leave the   
outer side of the vagus trunk4 ,each    
divides into a pretrematic and          
posttrematic branch2 a pharyngeal       
branch1 the last of which is the        
largest1 arises from each posttrematic4 
#d4 ,beyond the branchial nerves the    
remainder of the vagus passes backward  
as the intestinal or visceral trunk1 to 
the end of the pharynx1 where it divides
 into a number of branches which are    
distributed chiefly to the wall of the  
stomach4 ,near the point of this last   
division the vagus is crossed by the    
hypobranchial nerve1 which should be    
noted and preserved4  ,the occipital    
nerve penetrates the lateral wall of the
 cranium close behind the root of the   
vagus and enters the canal of the vagus1
 along which it passes4 ,on emerging1 it

 sends small branches to the nearby     
muscle1 while the principal portion runs
 on to join the hypobranchial nerve4    
,the occipital nerve will be found to   
arise from the ventral surface of the   
medulla1 below and behind the root of   
the vagus1 by two or more distinctly    
separated roots1 which may represent    
distinct nerves4  ,,spinal ,,nerves4    
,the spinal nerves are those nerves     
which arise from the sides of the spinal
 cord4 ,they differ from the cranial    
nerves not only in their origin outside 
the cranium1 but also in that each      
spinal nerve arises by two roots which  
spring from the spinal cord near the    
dorsal and ventral surfaces4 ,each root 
passes through a foramen in the         
cartilaginous wall of the neural canal1 
the ventral a little anterior to the    
dorsal1 after which they unite to form  
the spinal nerve4 ,between the junction 
of the roots and its foramen the dorsal 
root contains a mass of ganglion cells1 
which cause an enlargement known as the 

dorsal root ganglion4 ,the typical      
course of a spinal nerve is around the  
body to the ventral surface1 giving off 
branches to the muscles and skin of its 
segment4 ,a short distance from the     
vertebral column the spinal nerves lie  
just outside the peritoneum1 through    
which many of them can be seen and      
followed to about the level of the      
lateral vein4 ,at this point they pass  
outward into the muscles of the body    
wall4 ,to dissect any of the spinal     
nerves make a longitudinal incision     
along the lateral line and separate the 
dorsal muscle mass from the lateral     
muscles for some distance4 ,the dorsal  
muscles can then be pressed toward the  
vertebral column and dissected away from
 the peritoneum4 ,the spinal nerves1    
lying against the peritoneum1 will be   
exposed and can be followed easily1     
first to their roots1 next ventrally4   
,the hypobranchial nerve1 to which      
attention was called at the point where 
it crosses the vagus1 is formed by the  

union of the principal branches of the  
occipital and first two spinal nerves4  
,the third spinal nerve receives a      
branch from the second1 and itself      
accompanies the hypobranchial nerve     
closely without actually becoming a part
 of it4 ,the union of nerves thus formed
 is known as a plexus4 ,after crossing  
the vagus the hypobranchial nerve forks1
 one division passing medial to1 the    
other lateral to the anterior cardinal  
vein2 both run ventrally1 following the 
last gill arch1 and reunite on the      
lateral wall of the pericardium1 forming
 a trunk which runs forward4 ,at the    
anterior end of the pericardium this    
divides into a dorsal and a ventral     
branch which innervate the surrounding  
muscles4 ,the hypobranchial nerve       
innervates the skin of the region       
immediately in front of the pectoral    
girdle1 and the coraco-arcualis         
communis1 coraco-mandibularis1          
coracohyoideus1 and coraco-branchialis  
muscles4  ,the third1 fourth1 fifth and 

sixth spinal nerves pass backward and   
ventrad till they reach the level of the
 articulation of the pectoral fin with  
the girdle4 ,here they join to form a   
simple brachial plexus1 from which arise
 branches proceeding to the musculature 
of the dorsal and ventral faces of the  
fin4 ,the seventh to eleventh spinal    
nerves pass downward to the level of the
 fin1 and then branch1 one portion      
entering the muscles of the ventral body
 wall1 while the other passes into the  
depressor muscles of the fin4  ,the     
pelvic fin is innervated by eight or    
nine spinal nerves which pass backward  
and downward along the medial edge of   
the septum between the myomeres1        
entering the dorsal side of the fin     
along its axis4 ,no plexus is formed4   
,,olfactory ,,organ 7,,nasal ,,sac74    
,dissect away the skin and other tissues
 around the nostril so as to expose     
completely the olfactory organ2 this    
will be found to be a dark-colored1     
nearly spherical mass1 of half the      

diameter of the eye1 firmly attached at 
its base4 ,by cutting away the cartilage
 dorsal to the nasal sac its base will  
be exposed1 and the olfactory bulb will 
be shown to be closely adherent to a    
considerable part of the postero-dorsal 
surface of the organ4 ,numerous short   
nerves can be demonstrated to pass from 
the olfactory bulb into the olfactory   
organ2 all these nerves together are    
considered as the first cranial or      
olfactory nerve4 ,remove the olfactory  
organ from the head2 divide it by a     
median longitudinal cut2 observe the    
arrangement and structure of its double 
series of internal folds 7lamellae71 and
 the complete median septum4  ,,ventral 
,,surface ,,of ,,the ,,brain4 ,cut the  
cord in two some distance back of the   
brain4 ,cut all cranial nerves just     
inside the cranium and carefully lift   
the brain out4 ,parts of the ventral    
portion of the brain lie in a recess    
beneath the mesencephalon and must be   
disengaged very gently4  ,identify and  

examine the ventral parts of the brain4 
,note the considerable lateral          
compression of the mesencephalon4 ,the  
optic nerves cross beneath the          
diencephalon1 forming the optic chiasma4
 ,from the sides of the chiasma slightly
 elevated optic tracts1 formed by the   
fibres of the optic nerves1 can be      
traced into the optic lobes4  ,back of  
the optic chiasma the projecting ventral
 portion of the diencephalon forms the  
hypothalamus4 ,the posterior lobe of    
this structure is the hypophysis or     
pituitary body4  ,the oculo-motor nerves
 emerge over the posterior end of the   
hypothalamus4  ,the ventral portion of  
the mesencephalon is formed by the      
cerebral peduncles 7crura cerebri71     
columns of fibres passing between the   
myelencephalon and telencephalon4  ,the 
abducens nerves arise on the ventral    
surface of the myelencephalon near the  
midline and just back of a line         
connecting the roots of the auditory    
nerves4  ,the internal carotid arteries 

reach the brain at the sides of the     
hypothalamus4 ,branches are sent upward 
and forward over the surface of the     
brain4 ,anastomoses between the vessels 
of the opposite sides are formed        
anterior to the optic chiasma4 ,the main
 branches of the carotids pass backward 
along the sides of the hypothalamus and 
unite behind this organ4 ,the median    
artery thus formed runs along the       
ventral surface of the myelencephalon   
and the spinal cord4 ,numerous          
transverse vessels are given off to the 
myelencephalon4  ,identify the roots of 
the remaining cranial nerves4           
,,cavities ,,of ,,the ,,brain4 ,divide  
the brain into exactly equal halves by a
 vertical longitudinal cut4  ,each lobe 
of the prosencephalon contains a large  
cavity4 ,these are the prosocoels4 ,they
 are commonly known either as the       
lateral ventricles1 or the left cavity  
as the first ventricle and the right as 
the second ventricle4 ,the prosocoels   
are continued into the olfactory lobes1 

these portions being known as           
rhinocoels4  ,the thalamocoel is the    
cavity within the diencephalon1 often   
called the third ventricle4 ,the        
prosocoels communicate with the         
thalamocoel by lateral openings1 the    
foramina of ,monro4 ,the roof of the    
thalamocoel is very thin and is         
non-nervous2 it is frequently torn      
during the early dissection4 ,where the 
lobes of the prosencephalon meet the    
dorsal wall of the diencephalon this    
thin roof is pushed into the prosocoels1
 carrying with it the pia mater and its 
blood vessels1 and thus forms vascular  
ingrowths known as the choroid plexi4   
,the thalamocoel continues above into   
the epiphysis and below into the        
hypothalamus4  ,the myelocoel is the    
large cavity of the myelencephalon4 ,it 
also is frequently apparently open to   
the exterior at the posterior end by the
 accidental breaking of the thin1       
non-nervous dorsal wall of this region4 
,the myelocoel is also known as the     

fourth ventricle4  ,the thalamocoel and 
myelocoel are connected by a narrow     
passage through the mesencephalon1 the  
aqueduct of ,sylvius 7iter1 mesocoel74  
,the optocoels are large cavities within
 the optic lobes which open into the    
aqueduct of ,sylvius4  ,a large metacoel
 in the metencephalon opens into the    
myelocoel4 ,the myelocoel is also       
continued into the corpora restiforma2  
posteriorly it joins the central canal  
which extends down the center of the    
spinal cord4  ,,dissection ,,of ,,the   
,,eye4 ,remove one of the eyes from its 
orbit1 and divide it into inner and     
outer halves by an equatorial cut around
 the eyeball 7not directly through it1  
as this tears the lens from its         
fastenings74 ,place the halves under    
water and observe3  ,in the inner half3 
,the posterior chamber1 the cavity of   
the eyeball which has been opened4      
,during life it is filled by a          
gelatinous substance1 the vitreous      
humor4  ,the retina1 a delicate         

yellowish-white membrane lining the     
interior of the eye1 loosely attached to
 the outer coats except at the point of 
entrance of the optic nerve4  ,the      
choroid coat1 a thin1 black membrane    
outside the retina4 ,it can be pulled   
away from the outer coat quite easily   
except near the optic nerve4  ,the      
sclerotic coat1 the outer coat of the   
eye4 ,this is composed of connective    
tissue having an almost cartilaginous   
consistency1 is only slightly pigmented1
 and is somewhat translucent4 ,the      
muscles of the eye are inserted upon the
 sclerotic4  ,in the outer half3  ,the  
ora serrata1 an irregular line along    
which the retina ends4  ,the iris1 a    
fold of the choroid extending inward    
like a shelf1 and perforated centrally  
to form the pupil4 ,around the iris the 
choroid is folded radially into the     
ciliary processes4  ,the lens1 a        
spherical body1 transparent and elastic 
during life1 but opaque and hard in     
preserved specimens4 ,it projects into  

the pupil and is suspended from the     
ciliary processes by a delicate         
membrane1 the suspensory ligament4  ,the
 anterior chamber1 in front of the iris 
and lens1 filled with a watery fluid1   
the aqueous humor4  ,the transparent    
cornea1 forming the outer side of the   
eyeball1 continuous with the sclerotic4 
,take out the other eye and cut it in   
two by a section through the pupil and  
optic nerve4 ,review the relation of the
 parts4                                 
,,the ,,skeleton  ,there seems to be no 
easy way of cleaning the skeleton of    
dogfish which have been preserved in    
formalin or alcohol1 the only procedure 
being to cut1 pick1 and scrape the flesh
 away from the skeleton4 ,time and      
patience are required1 but if these are 
allowed there is no reason why all the  
parts of the skeleton cannot be         
thoroughly studied4 ,specimens which    
have been preserved in brine are more   
easily skeletonized4  ,the skeleton is  
entirely composed of cartilage which1 in

 large species of elasmobranchs and in  
old individuals of small species1       
becomes impregnated with lime salts1 in 
some cases to such an extent as to      
resemble soft bone4  ,the parts of the  
skeleton are frequently grouped under   
two heads3 the axial skeleton1          
comprising the skull and vertebral      
column2 and the appendicular skeleton1  
including the pectoral and pelvic       
girdles and the skeleton of the fins4   
,,vertebral ,,column4 ,the vertebral    
column is divided into two regions1     
thoracic and caudal1 distinguished by   
the slightly different character of the 
vertebrae4 ,remove the muscle and       
connective tissue from the vertebral    
column for a short distance anterior to 
the first dorsal fin4 ,care is required 
not to cut away small cartilages        
occupying the positions of ribs4 ,now   
remove from the body about two inches of
 the portion of the column exposed with 
any cartilaginous parts which may be    
attached to the vertebrae4 ,the vertical

 column is made up of segments1 called  
vertebrae4 ,each vertebra consists of a 
large ventral mass1 the centrum1 and an 
arch1 the neural arch1 roofing over the 
dorsal surface of the centrum2 the arch 
is composed of several small plates of  
cartilage4 ,the opening enclosed by each
 centrum and its neutral arch is the    
vertebral foramen2 the joined vertebral 
foramina form the neural canal1 which is
 occupied by the spinal cord4  ,separate
 one of the vertebrae from the rest4    
,the centrum is deeply concave at each  
end2 such a centrum is termed           
amphicoelous4 ,at the middle of the     
centrum the concavities meet and thus a 
canal is formed through it4 ,this canal 
and the spaces between the ends of      
adjoining vertebrae are filled by the   
remains of the notochord1 a rather pulpy
 structure extending from end to end of 
the vertebral column4  ,the concave     
faces of the vertebrae consist of much  
firmer cartilage than the remaining     
portions1 sometimes even calcified4     

,make a transverse section through the  
middle of a centrum and observe the     
relations of the parts4  ,on each side  
of the centrum1 near the ventral edge1  
is a plate-like projection1 the         
transverse process4 ,attached to the    
extremity of this is a slender          
cartilaginous rib4  ,each neural arch is
 made up of two distinguishable sets of 
plates4 ,the first consists of a pair of
 broad neural plates extending upward   
from each side of the centrum and       
uniting with each other dorsally4       
,between the neural plates of two       
successive vertebrae is a pair 7one on  
each side7 of intercalary plates which  
also unite over the neural canal4 ,the  
intercalary plates are over the joint   
between the centra4 ,neural and         
intercalary plates together make the    
lateral and dorsal walls of the neural  
canal4 ,the relations of these plates   
can sometimes be seen best when the     
neural arch is cleaned1 then cut away   
from the centrum1 and looked through    

toward the light4  ,in the lower part of
 each neural plate is a small foramen   
which allows the passage of the ventral 
root of the spinal nerve4 ,a foramen for
 the dorsal root is found at about the  
middle of the intercalary plate4  ,clean
 and remove some of the caudal vertebrae
 from the region just back of the       
cloaca4 ,in general they have nearly the
 same structure and relations as the    
thoracic vertebrae1 but have no         
transverse processes and the plates of  
the neural arches are not so distinct4  
,there is also added a ventral arch     
similar in form to the neural arch4     
,this is the haemal arch1 in which lie  
the caudal aorta and vein4 ,its roof is 
the surface of the centrum1 the sides   
are formed by pairs of plates which     
correspond in number to the centra1 and 
unite with each other ventrally4        
,between the successive plates are      
openings for the passage of branches of 
the artery and vein4  ,in this region   
foramina for the roots of the spinal    

nerves are found only in every other    
pair of neural and intercalary plates4  
,toward the tip of the vertebral column 
the relation of the neural and          
intercalary plates to the centra becomes
 very irregular4  ,in ,eugaleus the roof
 of the neural arch is formed by a row  
of small1 diamond-shaped plates which   
fit in between the other two sets4 ,as  
these plates correspond morphologically 
to the neural spines of higher          
vertebrates1 they may receive that name 
here4 ,it is probable that the dorsal   
portion of the arch in ,squalus is      
composed of similar neural spine        
elements which have become fused with   
the neural and intercalary plates of    
each side4  ,,skull4 ,the skull is      
entirely cartilaginous1 and comprises   
three principal divisions3 7#a7 the     
cranium1 an undivided mass of cartilage 
lodging the brain and the organs of     
smell1 sight1 and hearing2 7#b7 the     
jaws2 7#c7 the visceral arches1 or      
skeletons of the gill arches4  7#a7 ,the

 cranium4 ,a blunt prolongation of the  
anterior extremity of the cranium forms 
the rostrum1 which supports the soft    
tissues of the snout4 ,at each side of  
the base of the rostrum the cranium     
widens abruptly4 ,on the anterior face  
of the widened portion and below the    
posterior angles of the rostrum is a    
pair of protruding olfactory capsules1  
in which the olfactory sacs are         
enclosed4 ,an oval aperture in the      
posterior wall of each capsule opens    
into the braincase and permits the      
passage of the olfactory nerve through  
the cranium4  ,back of the olfactory    
capsules are large lateral cavities1 the
 orbits4 ,the dorsal edge of the orbit  
makes an overhanging ledge1 known as the
 supra-orbital crest4 ,the projecting   
anterior and posterior angles of the    
orbit are distinguished as the prae- and
 postorbital processes4  ,the portions  
of the cranium back of the orbit and at 
the sides of the braincase form large   
lateral projections 7auditory capsules7 

containing the organs of hearing4  ,at  
the center of the nearly vertical       
posterior surface of the cranium is a   
large opening1 the foramen magnum1      
through which the spinal cord passes4   
,at either side of and below the foramen
 magnum is a smooth articulatory surface
 7occipital condyle7 articulating with  
the centrum of the first vertebra4  ,the
 flattened ventral surface of the       
posterior part of the cranium forms the 
roof of the mouth1 or palate4  ,in the  
mid-dorsal line of the cranium1 between 
the prae-orbital processes1 is a small  
aperture opening into the brain cavity1 
the epiphysial foramen4 ,it is closed   
during life by a tough1 fibrous         
membrane4 ,the stalk of the epiphysis   
extends to the under surface of this    
membrane4  ,between the auditory        
capsules is a deep depression in the    
roof of the cranium in the floor of     
which can be seen the two small pores   
through which the ducti endolymphatici  
pass into the capsules4 ,close behind   

them are two larger openings for the    
perilymph ducts4  ,a pair of foramina   
passes through the inner edge of the    
prae-orbital process2 these permit the  
passage of the ophthalmic branches of   
the trigeminal and facial nerves to the 
dorsal surface of the snout4 ,near the  
bottom of the inner wall of the orbit is
 the foramen of the optic nerve4 ,in the
 postero-ventral angle of the orbit is  
the large trigemino-facial foramen for  
the exit of branches of the trigeminal  
and facial nerves2 in front of it is the
 small oculo-motor foramen4 ,the        
extremely small foramen of the trochlear
 nerve is almost directly above the     
optic foramen1 near the top of the inner
 wall of the orbit4 ,close below the    
trigemino-facial foramen is the small   
passage for the abducens nerve4 ,below  
the abducens foramen is the transbasal  
canal4 ,behind and below the            
trigemino-facial foramen are two        
foramina1 through which pass the        
hyomandibular branches of the facial    

nerve4 ,the foramen of the vagus nerve  
is close to the foramen magnum1 upon the
 posterior surface of the cranium4 ,the 
foramen of the glossopharyngeal nerve is
 lateral to that of the vagus1 near the 
postero-lateral angle of the cranium4   
,the cranium of ,eugaleus is much like  
that of ,squalus1 except that the       
rostrum is formed by three rods1 two    
dorsal and one ventral1 which arise from
 the front of the braincase and converge
 anteriorally until they meet and fuse4 
,the olfactory capsules are much larger 
and of heavier cartilage than in        
,squalus4 ,the auditory region similarly
 is more prominent4  7#b7 ,the jaws4    
,the jaws in reality are the first pair 
of visceral or gill arches1 and in spite
 of the modification which has taken    
place this relation can be seen easily  
in the adult shark4 ,the upper jaw      
consists of a pair of palato-quadrate   
cartilages1 united medially by ligament1
 and bearing the upper series of teeth4 
,a large hooked palatine process extends

 from each palato-quadrate cartilage    
upward along the inner wall of the      
orbit4 ,the lower jaw likewise consists 
of a pair of ,meckel's cartilages1      
united medially 7the union is called the
 symphysis71 and bearing the lower      
series of teeth4 ,a pair of small labial
 cartilages1 which support the edges of 
the labial pockets1 lie at each corner  
of the mouth4  7#c7 ,visceral arches4   
,the first of the visceral arches is    
much larger and heavier than the rest4  
,it is known as the hyoid arch4 ,each   
side of the arch consists of two rods of
 cartilage3 7#a7 the hyomandibular      
cartilage1 which articulates with a     
distinct facet on the lateral surface of
 the auditory capsule1 and extends from 
here downward1 outward1 and backward2   
7#b7 the ceratohyal cartilage1 which is 
movably articulated to the hyomandibular
 and extends downward1 forward and      
inward4 ,the ventral ends of the        
ceratohyals are united by a median1     
plate-like basihyal4  ,the              

palato-quadrate and ,meckelian          
cartilages are suspended from the       
hyomandibular by several strong         
ligaments1 the direct attachments of the
 jaws to the cranium being of soft      
connective tissue only4 ,both the       
hyomandibular and ceratohyal cartilages 
bear slender rods 7branchial rays7 on   
their posterior edges1 which support the
 anterior wall of the first gill pouch4 
,note the position of the spiracle      
between the mandibular and hyoid arches4
 ,the anterior wall of the spiracle is  
strengthened by two small1 flat1        
vertical cartilages1 probably homologous
 with the branchial rays of the gill    
arches4  ,the remaining five visceral   
arches differ little in their           
construction4 ,dorsally1 each has a     
flat1 sickle-shaped pharyngo-branchial  
cartilage attached to the vertebral     
column by fibrous bands4 ,the           
pharyngo-branchials of the last two     
arches are fused4 ,ventrad to each      
pharyngo-branchial is an epibranchial   

cartilage4 ,the next segment of each    
arch is formed by the ceratobranchial   
cartilage4 ,all the epibranchials and   
ceratobranchials except those of the    
fifth arch bear slender branchial rays4 
,the ventral ends of the                
ceratobranchials articulate with each   
other1 the first being attached to the  
ceratohyal by ligament4 ,the second1    
third1 and fourth arches have another   
more ventral series of cartilages1 the  
hypobranchials4 ,the lower ends of the  
hypobranchials are attached to a large  
median plate1 the basibranchial4 ,the   
fourth ceratobranchial joins the third  
hypobranchial1 while the                
ceratobranchials of the fifth arch are  
attached to the basibranchial directly4 
,the basibranchial is composed of two   
segments closely united by ligament2 the
 anterior one narrow1 the posterior     
broad and flat in front1 tapering to a  
sharp point behind4  ,short teeth of    
cartilage1 called gill rakers1 project  
into the pharynx from the inner edges of

 the arches4  ,a dorsal and a ventral   
series of extra-branchial cartilages1   
thin1 slender plates1 lie on the        
external side of each gill arch4        
,,pectoral ,,girdle ,,and ,,fin4 ,remove
 from the body the pectoral girdle1 with
 the fins attached1 and carefully scrape
 off the muscles from the cartilaginous 
parts4 ,it will be found that the       
support of the fin is partly of         
cartilaginous plates and rods1 partly of
 horny fibres 7dermal fin-rays7 which   
overlie the extremities of the          
cartilages and extend to the edges of   
the fin4 ,these fibres are in two       
layers1 one beneath the skin of each    
side4 ,they are formed in the dermis4 ,a
 similar arrangement of horny fibres is 
found in all the other fins4  ,the      
pectoral girdle passes across the       
ventral surface of the body and upward  
on each side to the level of the        
vertebral column4 ,the stout ventral bar
 presents numerous facets for the origin
 and insertion of muscles4 ,the         

articular surfaces for the pectoral fins
 are well up on the sides of the girdle4
 ,the slender dorsal end of each side of
 the girdle consists of a separate bar  
of cartilage1 movably articulated to the
 lower portion4 ,the ascending limb of  
the girdle1 from the fin articulations  
to the base of the cartilage just       
mentioned1 is called the scapular       
portion2 the small bar is the           
supra-scapular2 the ventral bar between 
the fin articulations is the coracoid   
portion4  ,the cartilaginous skeleton of
 the pectoral fin consists primarily of 
a row of three basal cartilages1 all    
articulating proximally with the girdle4
 ,the middle basal is much the largest4 
,distal to the basals are three rows of 
rod-like radial cartilages1 the proximal
 row being articulated to the basals4   
,,pelvic ,,girdle ,,and ,,fin4 ,remove  
the pelvic girdle from the body with the
 pelvic fins attached1 and clean away   
the muscles4  ,the pelvic girdle        
consists of an almost straight bar of   

cartilage1 slightly thicker at its      
middle than at its ends1 which lies     
transversely in the ventral wall of the 
abdomen4 ,to each end is attached a long
 basal cartilage which lies in the fin1 
close to and parallel with its inner    
margin4 ,a proximal series of slender   
radial cartilages is attached to the    
lateral side of the basal2 a distal     
series of very short radials lies       
outside of the first series1 while the  
portion of the fin beyond these is      
supported by the dermal fin-rays4       
,,first ,,dorsal ,,fin4 ,remove the mass
 of muscles on both sides of the base of
 the fin down to the vertebral column4  
,the principal cartilages of the fin lie
 in the median connective tissue septum 
which separates the dorsal musculature  
of the two sides of the body4 ,the basal
 cartilages of the fin are attached to  
the vertebral column by means of this   
septum4 ,it is best to remove the       
underlying portion of the column with   
the fin4 ,the cartilages can then be    

scraped perfectly clean4 ,the skeleton  
of the fin is composed of three rows of 
cartilages3 7#a7 a basal row consisting 
of one very large1 flat plate and two or
 three smaller ones posterior to it2    
7#b7 an intermediate row of several     
plates of nearly equal size2 and 7#c7 a 
distal row of several very small plates4
 ,the intermediate and distal rows      
extend beyond the body musculature into 
the base of the fin4 ,the remainder of  
the fin is supported by the dermal rays4
 ,in front of the cartilages which have 
been mentioned is the strong spine of   
dentine 7see p4 #e71 with its free      
portion sheathed by an enamel-like      
covering4  ,,second ,,dorsal ,,fin4     
,remove this from the body in the same  
manner as the first dorsal4 ,its        
structure follows the same general plan1
 the differences being minor ones of    
shape1 size1 and number of plates4      
,several thin cartilaginous plates are  
sometimes formed in the median septum in
 front of the spine4  ,,caudal ,,fin4   

,only one side of the caudal fin should 
be cleaned1 as when both sides are      
cleaned there is danger of breaking the 
delicate cartilages4 ,the cartilaginous 
skeleton of the caudal fin consists of a
 row of slender rods along the dorsal   
side of the vertebral column1 extending 
to its tip4 ,there are no cartilaginous 
elements in the fin ventral to the      
vertebral column4 ,by far the greater   
part of the caudal fin is supported by  
the two layers of horny fin-rays only4  
,,musculature  ,dissect the skin off the
 head1 neck1 and body to back of the    
pectoral fins4 ,observe first the       
musculature of the dorsal side of the   
neck and of the body back of the bases  
of the pectoral fins1 noticing that it  
is composed of narrow1 zigzag bands1    
called myomeres4 ,where these are fully 
developed they extend from the          
mid-dorsal to the mid-ventral line4     
,note carefully the relation of         
corresponding myomeres of the two sides1
 the exact course of a single myomere1  

and the direction of the muscle fibres  
in a typical myomere4 ,observe also that
 the muscles above the level of the     
vertebral column form a thick mass1     
which is frequently referred to as the  
dorsal musculature2 the muscle below    
this level may be correspondingly       
referred to as the ventral musculature4 
,as the muscles described below are     
dissected the mechanical effect of each 
should be determined4  ,,musculature    
,,of ,,the ,,head ,,and ,,neck4 ,on the 
lateral and ventral surfaces of the neck
 the primary relations of the myomeres  
are much modified by the development of 
numerous special muscles1 yet here and  
there traces of the metameric           
arrangement still show4 ,immediately    
beneath the skin is a thin sheet of     
muscle covering most of the ventral and 
lateral surfaces of the throat as far   
back as the pectoral girdle4 ,on the    
ventral surface a triangular space is   
left in front of the pectoral bar2 on   
the sides of the neck the sheet extends 

back to the last gill-cleft2 dorsally1  
it reaches to the upper extremities of  
the gill pouches4 ,this is the          
constrictor superficialis muscle4 ,it is
 attached to fasciae dorsally and       
ventrally1 and to the extra-branchial   
cartilages4  ,the constrictor           
superficialis consists of six metameric 
segments4 ,the four posterior ones are  
distinctly limited by the gill-slits and
 extra-branchial cartilages4 ,the second
 is anterior to the first gill slit1 the
 largest of all1 with distinct dorsal   
and ventral portions extending forward  
above and below the jaws4 ,the first is 
recognized as consisting of two distinct
 parts1 on the dorsal and ventral       
surfaces of the head4 ,the dorsal       
portion is a small curved muscle on the 
anterior wall of the spiracle1 extending
 from the external surface of the       
auditory capsule to the inner surface of
 the lower jaw4 ,it lies close against  
the levator marillae superioris 7see    
below74 ,on the ventral surface of the  

throat the posterior constrictor muscles
 of the two sides are separated by a    
large triangular area4 ,in front of this
 the ventral portions of the first and  
second constrictors meet in a median    
aponeurosis1 from which their fibres    
extend transversely1 those of the first 
to the mandibular cartilage1 those of   
the second to the hyoidean cartilage4   
,the first constrictor lies ventral or  
superficially to1 and largely covers the
 second4 ,reflect the first constrictor 
from the aponeurosis outward1 and       
demonstrate the two layers of muscle4   
,it will be noted that the second to    
sixth constrictors consist of united    
dorsal1 lateral and ventral portions1   
while the first is reduced to widely    
separated dorsal and ventral parts4  ,on
 each side of the head1 just outside the
 angle of the mouth1 is a large1 thick  
muscle arising from the lateral surface 
of the cranium1 and inserted upon the   
outer surface of the mandible1 the      
adductor mandibularis4  ,in front of the

 small dorsal constrictor superficialis 
#a1 and scarcely separated from it1 is  
the strong levator maxillae superioris1 
which extends from the lateral surface  
of the auditory capsule to the dorsal   
edge of the palato-quadrate cartilage4  
,eugaleus4 ,the dorsal portion of the   
constrictor superficialis #b reaches    
above the spiracle to the postorbital   
process4 ,reflecting it1 the adductor   
hyomandibulae is seen behind the        
spiracle1 arising from the upper part of
 the side of the auditory capsule and   
inserted on the end of the hyomandibular
 cartilage4 ,the levator palpebrae      
inferioris arises under the origin of   
the levator hyomandibulae1 and passes   
forward and downward between the        
spiracle and postorbital process1 to    
insert in the posterior end of the lower
 eyelid4 ,the depressor palpebrae       
superioris arises from the fascia dorsal
 to the spiracle1 passes mediad to the  
levator palpebrae inferioris1 upward and
 forward1 to insert in the posterior end

 of the upper eyelid4 ,remove these     
muscles4 ,the infra-orbital canal passes
 mediad to the muscles of the eyelids4  
,the levator maxillae superioris lies   
between the spiracle and the orbit4     
,behind it is a small slip of muscle    
extending from the anterior wall of the 
spiracle to the lateral surface of the  
auditory capsule which seems to         
represent the constrictor superficialis 
dorsalis #a4  ,a thin sheet of muscle   
covers the anterior face of each        
inter-branchial septum4 ,at the surface 
these pass into the constrictor         
superficialis1 and are evidently        
portions of the latter muscle1 though   
they are named the musculi              
interbranchiales4  ,above the           
constrictor superficialis1 lying on the 
side of the neck between it and the     
dorsal musculature1 is a broad trapezius
 muscle4 ,it arises from the fascia     
covering the lateral surface of the     
dorsal musculature4 ,its fibres pass    
obliquely downward and backward1 mediad 

to the posterior gill pouches1 to insert
 upon the anterior edge of the scapular 
portion of the pectoral girdle4 ,the    
anterior portion of the trapezius is    
also inserted upon the epibranchial of  
the fifth gill arch4  ,just in front of 
the mouth is a pair of strong muscles   
7levator labialis superioris71 each     
arising from the ventral surface of the 
cranium close to the median line4 ,they 
pass into strong tendons which are      
inserted among the fibres of the ventral
 portion of the adductor mandibulae4    
,the muscle mass in front of the mouth  
and the lower part of the adductor      
mandibularis thus form the two bellies  
of a digastric muscle1 with the tendon  
between them4  #b,remove the ventral    
portions of the first and second        
superficial constrictors and clear the  
mass of muscles lying between the       
coracoid portion of the pectoral girdle 
and the mandible4 ,immediately in front 
of the girdle are two large muscles1 the
 coraco-arcuales communes1 whose fibres 

run inward and forward4 ,these muscles  
cover the ventral surface of the        
pericardium1 to the wall of which their 
median fibres are attached1 while the   
lateral fibres are attached around the  
ventral ends of the gill arches4        
,footnote #b3    ,the                   
coraco-mandibularis1 coraco-hyodeus1    
coraco-arcualis communis1 and           
coraco-branchialis muscles should be    
dissected as a preliminary   operation  
to following the ventral aorta and its  
branches4  ,in front of the             
coraco-arcuales communes are three large
 longitudinal muscles4 ,the median1     
unpaired one1 arising from the fascia   
between the coraco-arcuales communes and
 inserted upon the posterior surface of 
the lower jaw1 is the                   
coraco-mandibularis4 ,the other two1    
which lie dorsal to and outside of the  
coraco-mandibularis1 are the            
coraco-hyoidei4 ,they arise from the    
fasciae covering the anterior ends of   
the coraco-arcuales communes and        

posterior parts of the                  
coraco-branchiales1 and insert upon the 
basihyal4  ,dissect out the             
coraco-mandibularis and coraco-hyoidei1 
noting particularly the form and place  
of origin of the latter4 ,dorsal to the 
coraco-hyoidei are the first divisions  
of the right and left coraco-branchialis
 muscles1 which arise from fascia       
covering the anterior ends of the       
coraco-arcuales communes1 and are       
inserted upon the ventral extremity of  
the ceratohyal cartilage4 ,notice that  
they pass dorsad to the anterior        
branches of the aorta1 and that the     
aorta itself can be exposed between     
them4  ,remove the coraco-arcualis      
communis by dissecting it from the      
pectoral girdle and reflecting it       
forward4 ,the other four divisions of   
the coraco-branchialis are now revealed1
 attached to the lateral surface of the 
pericardium and the lateral portion of  
the coracoid4 ,the divisions of the     
muscle are clearly separated only near  

their insertions4 ,the second1 third1   
and fourth coraco-branchials are        
attached to the hypobranchial cartilages
 of the second1 third and fourth        
visceral arches4 ,the fifth division is 
inserted upon the lateral portion of the
 basibranchial and the expanded medial  
end of the fifth ceratobranchial4  ,the 
first aortic branch passes ventral to   
the first coraco-branchial4 ,the second 
aortic branch passes between the first  
and second coraco-branchials4 ,the third
 aortic branch passes between the second
 and third coraco-branchials4 ,the      
fourth aortic branch passes between the 
third and fourth coraco-branchials4     
,expose the dorsal ends of the gill     
arches by clearing away muscles and     
other tissues between the gill pouches  
and the spinal column4 ,two sets of four
 small muscles 7interarcuales7 will be  
found connected with the branchial      
cartilages4 ,the second1 third and      
fourth medial interarcuales extend from 
the posterior surfaces of               

pharyngo-branchial cartilages #a1 #b1   
and #c1 to the dorsal surfaces of       
pharyngo-branchials #b1 #c1 #d1 and #e4 
,the first medial interarcuale arises   
from the under surface of the cranium   
and inserts on the upper end of the     
first pharyngo-branchial4  ,the lateral 
interarcuales lie immediately below the 
medials4 ,the first has a double origin1
 most of the fibres arising from the    
lower part of the posterior edge of the 
first pharyngo-branchial2 a smaller     
bundle from the anterior edge of the    
second pharyngo-branchial4 ,its         
insertion is along the dorsal surface of
 the first epibranchial cartilage4 ,the 
second and third lateral interarcuales  
are like the first1 but since the fourth
 and fifth pharyngo-branchials are      
fused1 the origin of the fourth lateral 
interarcuale is not divided4  ,the      
circular muscles of the oesophagus are  
strongly attached to the last           
pharyngo-branchial4  ,,musculature ,,of 
,,the ,,pectoral ,,fin4 ,the dorsal     

muscle of the fin 7levator-retractor7   
arises mostly from the scapular portion 
of the girdle1 with a small part arising
 from the fascia covering the lateral   
musculature of the body4 ,it is attached
 in fasciculi to the dorsal surfaces of 
the cartilaginous rays4 ,the ventral    
muscle 7depressor-protractor7 arises    
from the median portion of the girdle   
and is inserted upon the cartilaginous  
rays in similar fasciculi4 ,a portion of
 the lateral body muscles is inserted   
upon the scapular portion of the girdle4
  ,,musculature ,,of ,,the ,,pelvic     
,,fin4 ,ventral surface3 ,an adductor   
muscle has origin upon the              
postero-lateral edge of the girdle2 it  
is inserted upon the antero-medial      
surface of the basal cartilage of the   
fin4 ,the depressor muscle consists of  
small fasciculi1 each corresponding to a
 cartilaginous ray4 ,they arise from the
 postero-lateral surface of the basal   
cartilage and are inserted upon the     
distal extremities of the rays4  ,dorsal

 surface3 ,the abductor arises from the 
fascia covering the trunk muscles1 and  
inserts upon the fascia covering the    
intrinsic muscles of the dorsal side of 
the fin4 ,these latter 7levatores7 are  
arranged in exactly the same manner as  
the fasciculi of the depressor4         
,,musculature ,,of ,,the ,,dorsal       
,,fins4 ,a sheet of muscle is attached  
to each side of the anterior dorsal fin1
 extending nearly up to the bases of the
 dermal fin-rays4 ,this muscle passes   
downward between the dorsal body        
musculature of the two sides4 ,part of  
the fibres arise from the fasciae       
covering the medial surfaces of the body
 muscles1 part from the basal cartilage 
of the fin itself4 ,they are inserted   
upon the lateral surfaces of the broad  
cartilaginous fin-rays4 ,the muscles of 
the posterior dorsal fin are exactly    
similar in arrangement4  ,,musculature  
,,of ,,the ,,caudal ,,fin4 ,there is no 
special musculature for the dorsal      
portion4 ,a narrow1 band-like muscle is 

found on each side of the ventral       
portion1 widest above the triangular    
ventral lobe4 ,the fibres of this muscle
 arise upon the flattened1 expanded ends
 of the haemal spines4 ,they pass       
obliquely backward and upward to be     
inserted in the fascia underlying the   
skin4                                   
----------------------------------------
--------------------------------        
,transcriber's ,notes3      ,missing or 
obscured punctuation was silently       
corrected4      ,typographical errors   
were silently corrected4                
,inconsistent spelling and hyphenation  
were made consistent only       when a  
predominant form was found in this book4
      ,text that was in italics is      
enclosed by underscores 7italics74