NERVOUS SYSTEM. 



537 



Nervous System. 



The brain, covered with a darkly pigmented pia mater, 

 has the usual five parts. 



The elongated cerebral hemispheres have " olfactory 

 lobes " in front of them, and are connected by 

 anterior and posterior commissures, and by a hint 

 of a " corpus callosum " (?). 



The thalamencephalon gives origin dorsally to a pineal 

 outgrowth closely attached to the skull. On the 

 ventral side will be seen the chiasma or interlaced 

 crossing of the optic nerves, and a tongue-shaped mass 

 (the tuber cinereum), to which the pituitary body is 

 attached, and which is produced by the depression 



c.h 



/ 4~o 1. '»'■■'» 



Fig. 179. — Brain of Frog. {After Wiedersheim. ) 



I. Dorsal Aspect. — o.L, olfactory lobes ; c.h., cerebral hemi- 

 spheres ; Z'., pineal body, rising from optic thalami ; (7/./., optic lobes; 

 cb.^ rudimentary cerebellum ; Al.O., medulla oblongata. 



II. Vp:ntkal Asi'ECT. — The numbers Indicate the origins of the 

 nerves ; ck. optic chiasma ; T.c, tuber cinereum ; //., hypophysis. 



III. Longitudinal Sect[on.^ — i.v., 1 and 2, lateral ventricles of 

 cerebrum ; F.711., foramen of Monro ; V., 2, ^nd 4, third and fourth 

 ventricles ; Aq. cavities of optic lobes and aqueduct of Sylvius from 

 third to fourth ventricle. 



of the f^oor of the third ventricle to form the 



infundibulum. 

 The optic lobes, a pair of oval bodies between and below 



which is the iter. 

 The cerebellum, a very narrow transverse band. 



