64 THE NECTURUS 



eye. It is small and thread-like and must be traced care- 

 fully. Trace it to the eyeball. Note its origin on the 

 ventral side of the brain. (3) The oculomotor is also a 

 very small, threadlike nerve that extends out from the 

 mesencephalon to the eye muscles. Its origin should be 

 noted in the study of the ventral surface of the brain. 

 (4) (6) trochlear and abducens do not appear as separate 

 nerves in Necturus, but are incorporated in the trigeminal 

 nerve from which they extend to the eye. Trace the 

 branches of the fifth nerve to the muscles of eyeball. (5) 

 The trigeminal nerve leaves the brain at the anterior end 

 of the fossa rhomboidalis, extends out and expands into 

 the Gasserian ganglion. The ophthalmic branch supplies 

 the muscles of the eyes and a large second branch supplies 

 the jaws. Follow the branches to the muscles of the eye 

 and jaw. (7) The facialis leaves the skull with the audi- 

 tory, just posterior to the exit of the trigeminal. It sup- 

 plies the facial region and a part of the jaw musculature. 

 A branch from the trunk extends to the Gasserian gang- 

 lion. Trace the nerve out of the brain case to the regions 

 supplied. (8) The auditory nerve takes its exit from the 

 brain with the facialis, but separates immediately and goes 

 to the parts of the ear capsule to supply the inner ear. 

 It can be followed to the canals with a glass of low mag- 

 nification (X 3). (9) The glossopharyngeus comes from 

 the brain, just posterior to the auditory nerve. It extends 

 out from the medulla and joins shortly with the two roots 

 of the pneumogastric. The glossopharyngeus supplies the 

 gills, tongue and throat. (10) The pneumogastric or 

 vagus arises by two roots from the medulla, joining with 

 the glossopharyngeus to form a single trunk a short dis- 

 tance from the brain where the vagus ganglion is formed. 

 It may be dissected out so as to expose it to view. This 

 nerve supplies the heart and stomach. 



