NERVOUS SYSTEM OF SKATE 597 



fixed to the vertebral column. Its dorsal region is pro- 

 longed into an iliac process, while anteriorly a prepubic 

 process projects from the ventral (pubic) bar. The girdle 

 bears two articulating facets, to the posterior of which the 

 strong basal piece or metapterygium of the hind-limb is 

 attached. From this, and from the anterior facet of the 

 girdle, the jointed radials proceed. The claspers of the 

 males are closely connected with the posterior part of 

 the hind-limb, and have a complex cartilaginous skeleton 

 and an associated gland. 



The brain. — The brain (see Fig. 336) has the following 

 parts : — 



1. The fused cerebral hemispheres or prosencephalon, with a 



nervous roof, and without ventricles. 



2. The thalamencephalon or region of the optic thalami, with a 



thread-like pineal body above, infundibulum and pituitary 

 body below, thinly roofed third ventricle within. 



3. The mesencephalon or mid-brain, with the optic lobes above, 



the crura cerebri below, the iter passing between. 



4. The cerebellum, with an anterior and a posterior lobe, both 



marked by ridges and grooves. 



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 ; {b) the infundibulum, which carries the pituitary body ; 

 and (c) a thin-walled three-Iobed 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 verification, 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 th^e olfactory lobes of the 



covering fourth ventricle ; O.B., olfactory bulb ; O.C., olfactory 

 capsule ; S.O., superior oblique muscle ; E., eye ; S.R., superior 

 rectus ; E.R., external rectus ; S.O.VII., superficial ophthalmic 

 branch of VII. ; S.O.V., superficial ophthalmic branch of V. ; 

 O.P., ophthalmicus profundus; A.C., auditory capsule; 

 B.PL, brachial plexus ; R.F., recurrent facial ; C.T., chorda 

 tympani ; P.P., facial proper ; Hy., hyoidean ; Hyonin., 

 hyomandibular ; E.M., external mandibular ; M.M., man- 

 dibular muscle ; S^., spiracle ; P-s/^., prespiracular ; P/. , pala- 

 tine ; O.S., outer buccal ; Mn., mandibular ; Ma;., maxillary ; 

 I.B., inner buccal ; L., lateral branch of ^Y. ; Py., pyloric 

 branch ; C, cardiac branch. 



