j io ZOOTOMY. 



ventral ends of the clavicles and the muscles in connection 

 with them. 



115. The heart (Fig. 32), consisting of (a) the small, 

 thin-walled sinus venosus (s. v), attached by the hepatic 

 veins ( 125) to the pericardio -peritoneal septum; (b) the 

 large, irregular thin-walled auricle (aii), situated in the 

 dorsal region of the cavity, and largely concealing (c) the 

 firm, prismoidal ventricle (v), which lies in the ventral 

 region of the pericardial cavity and passes in front into (d) 

 the white, rounded bulbus arteriosus (b.a). 



1 1 6. The pericardium, a thin membrane lining the 

 pericardial cavity and reflected over the heart in the same 

 manner as the peritoneum over the abdominal viscera. 



XX. Skin the top of the head and clear away the 

 muscles until the roof of the skull is exposed : 

 break away the latter, bit by bit, with bone forceps 

 or strong scissors, and observe 



117. The brain, lying loosely in the large cranial 

 cavity, and continuous posteriorly with the spinal cord, 

 which passes through the neural canal of the vertebral 

 column to the tail. 



118. The arachnoid fluid filling the space between the 

 brain and the walls of the cranial cavity. 



Large pod are often killed by a blow on the head ; this gives rise to 

 extensive extravasation, and the cranial cavity is found to be full of 

 clotted blood, which adheres so closely to the brain as to require care in 

 its removal. 



XXL If no second specimen is to be dissected, go over 

 XXXVI 196 : then cut through the spinal cord 

 about half an inch from its junction with the 

 brain, sever the various cranial nerves, carefully 

 detach the olfactory lobes from their attachments 

 ( 189), remove the brain, and place it in alcohol 



