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MANUAL OF ELEMENTARY ZOOLOGY 



cephalon and the cerebral hemispheres. The thalamen- 

 cephalon lies immediately in front of the mid-brain. Its 

 sides are thick and are known as the optic thalami; its 

 roof and floor are thin. The floor is prolonged into a 

 hollow structure known as the infundibulum, to the end of 

 which is applied a glandular, non-nervous mass called the 

 pituitary body or hypophysis. The roof is prolonged into a 



Fig. 38. — The brain of a frog.— After Wiedersheim. 



I. Dorsal Aspect. — o. I., Olfactory lobes; c.A. t cerebral hemispheres; 

 P.y pineal stalk, rising from region of optic thalami; op.L, 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 (infundibulum); 

 H.. pituitary body or hypophysis. 

 III. Horizontal Section. — Lv. 1 and 2, lateral ventricles of cerebrum; 

 F.m., foramen of Monro; V.i and 4, third and fourth ventricles; 

 Ag., cavities of optic lobes and aqueduct from third to fourth 

 ventricle. 



short, hollow stalk, which in the tadpole is connected with 

 a structure known as the pineal body. In the adult this 

 has become separated and lies outside the skull. In 

 certain other animals the pineal body is much more highly 

 developed and still connected with its stalk, and its 

 structure shows that it is the remnant of a middle eye, 

 though it is no longer functional. In front of the pineal 

 stalk lies an anterior choroid plexus. The cavity of the 

 thalamencephalon is deep but narrow, and is known as the 

 third ventricle. It is bounded in front by a wall known as 



