248 THE DOG-FISH 



10. The pneumogastric or vagus is a large nerve, which 

 arises by a number of roots from the side of the 

 hinder part of the medulla, the most anterior root 

 being immediately behind and dorsal to that of the 

 glosso-pharyngeal. 



The nerve, formed by the union of these roots, 

 runs outwards and backwards through the skull - 

 wall, emerging at its hinder end between the cranium 

 and the auditory capsule. It then runs horizontally 

 backwards parallel to the vertebral column, and a 

 short distance to its outer side, lying along the inner 

 wall of the anterior cardinal sinus. It gives off 

 numerous branches, of which the principal ones are 

 the following. 



i. The branchial nerves, which are four in number, 

 run backwards and outwards in the floor of 

 the cardinal sinus to the upper ends of the 

 four hinder, i.e. second to fifth, branchial clefts. 

 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. 



Press away the medulla from the skull-wall to see the 

 roots of origin of the vagus. Slice away horizontally the 



