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 



1.V.2 



op.l- 



cb 



V-4 



III 



FIG. 179. Brain of Frog. (After WIEDERSHEIM.) 



I. DORSAL ASPECT. o.l., olfactory lobes; c.h., cerebral hemi- 

 spheres ; />., pineal body, rising from optic thalami ; op. I., optic lobes ; 

 cb., rudimentary cerebellum ; M.O., medulla oblongata. 



II. VENTRAL ASPECT. The numbers indicate the origins of the 

 nerves ; ch. optic chiasma ; T.c., tuber cinereum ; ff., hypophysis. 



III. LONGITUDINAL SECTION. l.v., i and 2, lateral ventricles of 

 cerebrum ; P.m., foramen of Monro ; K, 3 and 4, third and fourth 

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

 third to fourth ventricle. 



of the floor 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. 



