256 THE DOG-PISH 



Each then divides into a smaller anterior and a. 

 larger posterior branch, which supply the two 

 borders of the corresponding cleft, in a manner 

 precisely similar to that in which the glosso- 

 pharyngeal supplies the first branchial cleft. 



ii. The visceral nerves are continuations backwards 

 of the trunk from which the branchial nerves 

 arise ; they give off several branches, of which 

 the most important are the cardiac nerves 

 to the heart, and the gastric nerves to the 

 stomach. 



iii. The nerve of the lateral line arises from the 

 vagus near its root: it lies dorsal to the 

 branchial nerves, and behind these it runs 

 along the inner surface of the body- wall to the 

 hinder end of the body, parallel to the lateral 

 line, the sense-organs of which it supplies. 



D. Dissection of the Brain. 



1. Removal of the brain. 



Cut across the medulla a short way behind the roots of the 

 vagus. Gut through the olfactory nerves so as to separate the 

 olfactory lobes from the nasal capsules ; and cut through the 

 several cranial nerves one by one, about midway between the 

 brain and the skull-wall. Turn out the brain from the cranium, 

 taking care not to damage the pituitary body : this latter lies 

 on the under surface of the brain, opposite to the optic lobes, 

 and in a hollow of the skull-floor, to which it is firmly at- 

 tached, and from which it must be dissected away. 



Examine the skull after removal of the brain, and identify 

 the several nerve-stumps and their foramina of exit. 



2. The ventral surface of the brain. (Of. p. 247.) 



Place the brain in spirit, with the ventral swrface wpwa/rds, 

 and identify the following structures. 



a. The prosencephalon is marked by a shallow median 

 groove ; posteriorly it is directly continuous with 

 the thalamencephalon. 



