CRANIAL NERVES. 485 



VI. The abducens, a slender nerve, arising near the mid- 

 ventral line, adjacent to V. and VIII., and hidden 

 by the former, supplies the external rectus muscle 

 of the eye. 



VII. The facial^ morphologically the nerve of the spir- 

 acular cleft, supplies all the five groups of 

 ampullae on the head, and has seven main 

 branches. 



1. The ophthalmicus superficialis runs over and past 



the eye, unites with a similar branch of V., and 

 supplies ampullae on the snout. 



2. The inner buccal runs under the eye, through the 



nasal capsule, to inner buccal ampullae. The 

 outer buccal runs under the eye, over the antor- 

 bital cartilage, to outer buccal ampullae. 



3. The hyomandibular runs directly outwards behind 



the spiracle to hyoid ampullae. 



4. The external mandibular runs behind and under 



the spiracle along the jaw to mandibular am- 

 pullae, and is a branch of the hyo-mandibular. 



5. The palatine runs over the spiracle to the roof of 



the mouth. 



6. The "facial proper" supplies the muscles of the 



hyoid arch, and gives off 



7. The " chorda tympani," which runs under the spir- 



acle to the inner side of the jaw. 

 With the loss of the sensory ampullae, the seventh 



nerve of higher Vertebrates becomes restricted to 



the last three branches. 

 A recurrent branch of the facial also runs under 



the auditory capsule to IX., and is equivalent to 



Jacobson's anastomosis in higher forms. 



VIII. The auditory, arising just behind VII., is the nerve 



of the ear. 



IX. The glossopharyngeal, the most typical of all, is the 

 nerve of the first functional gill cleft. Its root 

 passes through the floor of the auditory capsule, 

 and bears a ganglion above the cleft. Its 

 branches, as named by Beard, are : 



(a) Post-branchial, to the muscles of the first branchial 



arch ; 



(b] prae-branchial, arches over the cleft and runs along 



its front wall ; 



(c] intestinal or visceral, to the pharynx ; 



(d) supra-branchial or dorsal to a few sense organs on 



the mid dorsal line of the head. 



