282 THE DOG-FISH. 



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, 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, bran- 

 chial clefts. Each then divides into a smaller 

 anterior 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 fine, the sense-organs of which it supplies. 

 It is probably to be associated with the seventh 

 nerve. 



