798 



PHYLUM CHORDATA : CLASS MAMMALIA 



the optic, nerves cross in a chiasma, from which optic tracts can be 

 traced to the optic lobes. Immediately behind the infundibuknn hes 

 a rounded elevation, called the mammillary body. Anteriorly, on the 

 ventral surface of each side of the thalamencephalon, there is a rounded 

 swelling, called the corpus geniculatum. The roof of the third 



Fig. 478. — Dorsal view of 

 rabbit's brain. 



olf.l., Olfactory lobes ; c.h., cere- 

 bral hemispheres ; o.L, optic 

 lobes (corpora quadrigemina), 

 shown by pressing outwards 

 the ix)sterior parts of the 

 hemispheres; c6., median part 

 of cerebellum ; FL, flocculus 

 of cerebellum ; 10, root of 

 the tenth or vagus nerve ; 

 s.c, spinal cord. 



Fig. 479. — Under surface of rab- 

 bit's brain. — After Krause. 



olf.l., Olfactory lobes ; o.t., olfactory tract ; 

 /./., frontal lobe of cerebral hemisphere ; 

 ch., optic chiasma ; I.e., infundibulum ; 

 cm., corpus mammillare ; 3, root of 

 oculomotor ; 4, root of pathetic ; 5, 

 root of trigeminal ; 6, root of abducens ; 

 7-8, roots of facial and auditory ; Fl., 

 flocculus of cerebellum : 9, root of glosso- 

 pharyngeal ; 10, roots of vagus ; H., 12th, 

 or hypoglossal ; p.v., pons Varolii 



ventricle is formed by a thin membrane or velum, with a plexus of 

 blood vessels. In the anterior wall of the third ventricle lies the small 

 anterior commissure : across the third ventricle the large middle com- 

 missure runs ; in the roof of the hind part of the ventricle lies a small 

 posterior commissure. 



