40 



(h) The club-shaped olfactory lobes, projecting forwards from the 

 cerebral hemispheres. 



(c) The corpora quadrigemina, (optic lobes), only partly seen below 

 the cerebral hemispheres posteriorly. 



{(1) The pineal body, above the corpora quadrigemina, and immediately 

 posterior to the cerebral hemispheres. 



(e) The cerebellum, large and tri-lobed. Turn back the anterior 

 portion of the cerebellum in order to expose the corpora quadrige- 

 mina and the valve of Vieussens, a thin layer of nervous tissue 

 stretching between the corpora quadrigemina and the cerebellum, 

 and forming the roof of the anterior portion of the fourth 

 ventricle. Note the pathetic (4th cranial) nerve arising from 

 the dorsal surface of the valve of Vieussens near the middle line 

 and looping round the brain towards the ventral surface. Note 

 the fioccular lobes at the outer aspect of the lateral lobes. 



(/) The medulla oblongata, seen on turning forwards the cerebellum. 

 Note — 



(1) The choroid plexus (tele vasculose) of the fourth ventricle, a 



portion of the pia mater covering the roof of the ventricle. 



(2) The dorsal pyramids, on either side of the dorsal fissure of 



the spinal cord. 



(3) The restiform bodies, external to the dorsal pyramids. 



(4) The fourth ventricle, its posterior portion seen on removing 



the choroid plexus. 

 3. On the ventral aspect of the brain observe — 

 (a) The olfactory lobes. 



(6) The cerebral hemispheres, divided by a ventral longitudinal groove 

 into a larger superior, and a smaller inferior, lobe. A slight de- 

 pression on the ventral aspect of the superior lobe represents the 

 fissure of Sylvius. 



(c) The optic tracts, optic commissure, and optic nerves. Trace the 



optic tracts backwards towards the corpora quadrigemina. 



(d) The infundibulum, a funnel-shaped projection to which the pituitary 



body is attached. 



(e) The corpus albicans (corpus mammillare), a rounded mass immedi- 



ately behind the infundibulum. 

 (/) The crura cerebri, or peduncles of the cerebrum, two broad bands 



diverging from the middle line posteriorly in front of the pons 



Varolii. Note the origin of the oculo-motor nerve (3rd cranial) 



from the ventral surfaces of the crura. 

 [g) The pons Varolii, two strong bands of transverse fibres running from 



the middle line outwards to the two halves of the cerebellum. 



Note the trigeminal (5 th cranial) nerve arising by two roots from 



the outer posterior margin of the pons. 



