178 ESSENTIALS OF ZOOLOGY 



to the skin of the dorsal region of the snout. The maxillary 

 (V 2 ) is also associated with the Vllth and runs along the floor 

 of the orbit to reach the integument in front of the mouth. 

 Both these branches are sensory. The mandibular (V 3 ) 

 accompanies the maxillary for some distance across the orbit 

 and leaves it to enter the mandibular muscles. This branch 

 is motor and is concerned in the innervation of the visceral 

 muscles of the mandible. The trigeminal is therefore a mixed 

 nerve, 



VI. Abducent. The abducent is a motor nerve which arises 

 from the floor of the medulla and enters the orbit to supply 

 the external rectus muscle of the eye. 



VII. Facial. The facial arises in close proximity to the 

 Vth in the facialis ganglion. The ganglion is connected to the 

 medulla, and distally it divides into an ophthalmic branch which 

 unites with V 1 , a large hyomandibular branch, a palatine 

 and inner and outer buccal branches. It is primarily the nerve 

 of the spiracle. The large hyomandibular passes outwards over 

 the hyomandibular cartilage, and when it approaches the lower 

 jaw it gives off, just under the spiracle, (1) two small branches to 

 the inner aspect of the lower jaw which represent the chorda 

 tympani of higher Craniates, and (2) its primary branch to the 

 hyoid muscles. It shortly after splits up into numerous 

 fibres which are distributed to the sensory canals of the hyoid 

 and mandibular regions. The palatine branch is directed to 

 the front of the spiracle, to which a prespiracular branch is 

 given off, and it passes forwards to supply the mouth epithelium, 

 ending in taste buds. The ophthalmic supplies the sensory 

 canals of the front of the head, the outer buccalis those of the 

 nasal region, and the inner buccalis the inner buccal sensory 

 canals. The nerve is sensory, being related to the sensory 

 canals of the head region and to sensory cells of the mouth 

 and spiracle, and it is also motor in connexion with the hyoid 

 musculature. 



VIII. Auditory. This nerve is sensory and originates in 

 the auditory ganglion, the fibres being directed on the one hand 

 into the medulla and on the other into the vestibule and 

 ampullae of the auditory organ. 



IX. Glossopharyngeal. The IXth nerve arises in a ganglion 



