'274 THE DOG-FISH. 



through the skiill-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 cardi- 

 nal sinus, and giving off numerous branches. 



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

 roots of origin of the vagus. Slice away horizontally the 

 hinder end of the skull to expose the nerve in this part of its 

 course. Lay open the anterior cardinal sinus by slitting up 

 its dorsal wall ; wash out the contained blood, and identify 

 the branches of the vagus running along its inner wall and 

 across its floor. Dissect these branches out, and follow them 

 to their distribution. 



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

 run backwards and outwards in the floor of 

 the anterior cardinal sinus to the upper ends of 

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

 clefts. Each then divides into a smaller an- 

 terior and a larger posterior branch, which 

 supply the two borders of the corresponding 

 cleft, just as the glosso-pharyngeal supplies 

 the two borders of the first branchial cleft. 



ii. The visceral or intestinal nerves are continua- 

 tions 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. 



The nerve of the lateral line arises dorsal to the 

 root of the ninth nerve. It runs backwards 

 above and to the inner side of the branchial 

 division of the vagus, continuing its course to 

 the hinder end of the body and parallel to 

 the lateral line, the sense-organs of which it 

 supplies. It is probably to be associated with 

 the seventh nerve. 



