598 PHYLUM CHORDATA I CLASS PISCES — FISHES 



cerebral hemispheres, extend to the nostrils, and 

 there expand in olfactory bulbs, which give off 

 small nerves to the nostrils. 

 II. The optic ^ leaving the region of the optic thalami, 

 cross in an optic chiasma, and extend to the 

 retina of the eye. 



III. The oculomotor or ciliary^ arising from the crura 



cerebri, near the mid-ventral line, supply four of 

 the six muscles of the eye. There is a ciliary 

 ganglion in connection with III., and also with 

 the ganglion of the ophthalmicus profundus. 



IV. The pathetic or trochlear are small nerves emerging 



dorsally from between the mid- and hind-brain, 

 and supplying the superior oblique muscles of 

 the eye. 

 V. The tregiminal, or nerve of the '' mouth-cleft," 

 arising from the medulla oblongata (as do all 

 that follow), has a (Gasserian) ganglion on its 

 root, and three main branches — the sensory 

 maxillary, which unites with the inner buccal 

 of VII. ; the motor mandibular, which inner- 

 vates the muscles of the jaws ; and the sensory 

 superficial ophthalmic (or orbitonasal), which 

 runs over the eye to the snout, closely united 

 (inside the same sheath) with a similar branch 

 of VII. 

 Parallel to these superficial ophthalmics, internal 

 to and above the inner buccal of VIL, there is 

 a ganglionated ophthalmicus profundus, which 

 sends branches to the eyeball, snout, etc. 

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

 mid-ventral line, adjacent to V. and VIII., and 

 hidden beneath the former, supplies the external 

 rectus muscle of the eye. 

 VII. The facial, the nerve of the spiracular cleft, 

 supplies all the five groups of ampullae on the 

 head, and has numerous branches. 



1. The ophthalmicus superficiahs runs over and past 



the eye, in intimate association with the similar 

 branch of V., and supplies ampullar on the snout. 



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



