i 8 VERTEBRATE ZOOLOGY 



roots of the trigeminus and passes through the same foramen with 

 this nerve into the orbit, to the external rectus muscle. The root 

 of this nerve will be seen when the ventral surface of the brain 

 is studied. 



7. The facial nerve arises in connection with the trigeminus. 

 It sends out three main branches,— the superficial ophthalmic, buc- 

 cal, and hyomandibular branches,— the first two of which enter 

 the orbit together with the trigeminus. The superficial ophthalmic 

 passes, together with the corresponding branch of the trigeminus, 

 along the medial wall of the orbit to the ophthalmic foramen and 

 from there to the Lorenzinian ampullae of the snout. The buccal 

 branch is joined with the maxillary branch of the trigeminus. The 

 hyomandibular branch is a large nerve which passes across the 

 hinder part of the orbit to the spiracle and the hyoid arch. 



8. The auditory nerve is a large, short nerve which arises in con- 

 nection with the trigeminal and facial nerves and almost at once 

 enters the auditory capsule. It is the shortest cranial nerve, and 

 the only one which remains within the cranium. It may be seen 

 by pressing the wall of the skull away from the brain. 



9. The glossopharyngeal nerve arises on the side of the medulla 

 some distance back of the auditory nerve. It may be seen by 

 pressing the wall of the skull away from the brain. It at once 

 enters a foramen in the inner wall of the auditory capsule and, 

 passing through the capsule, divides into two branches, which go 

 to the pharynx and the first gill arch. Near where it emerges from 

 the auditory capsule it contains a ganglionic swelling called the 

 petrosal ganglion. 



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

 by a number of roots on the side of the medulla near its dorsal 

 surface. It passes out of the skull at once by a foramen back 

 of the auditory capsule and runs back, as a broad band, along 

 the inner side of the gill arches, sending a large branch to each 

 of the hinder four arches. It also gives off, in front of these 

 gill nerves, the lateral-line nerve, which passes to the lateral line 

 and runs parallel to it to the hinder end of the body. The main 

 portion of the vagus, after giving off the gill nerves, is distributed 

 to the stomach. 



