CRANIAL NERVES. 483 



(5) The medulla oblongata, with thin vascular roof, with dorso- 

 lateral extensions called " restiform bodies." 

 The region beneath the thalamencephalon bears (a) two ovoid inferior 

 lobes, {]>) the infundibulum which carries the pituitary body, and (c) a 

 thin-walled three-lobed saccus vasculosus situated between the pituitary 

 body and the inferior lobes. 



Cranial Nerves} 



Owing to the flat form of the skate and its frequently large 

 size, the dissection of the cranial nerves is perhaps easier 

 than in any other Vertebrate. Expecting practical verifica- 

 tion, we shall describe their distribution in some detail, 

 following in regard to certain points the investigations of 

 Professor Cossar Ewart. 



I. The olfactory, rising from the olfactory lobes of the 

 cerebral hemispheres, extend to the nostrils, and 

 there expand in olfactory bulbs, which give off 

 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 octilomotor 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 arising 

 dorsally froin between the mid and hind brain, 

 and supplying the superior oblique muscles of the 

 eye. It is possible that they really belong to V. 

 V. The trigeminal, or nerve of the " mouth-cleft," aris- 

 ing 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 innervates the muscles 

 of the jaws ; and the sensory superficial ophthal- 

 mic (or orbitonasal), which runs over the eye to 

 the snout, and comes into close relations with a 



' I have to acknowledge indebtedness to Dr. Beard for his liindness in 

 helping me to state the distribution of these nerves correctly, or as cor- 

 rectly as is at present possible. 



