354 DISSECTION OF THE RABBIT 



connecting the hinder border of the optic 

 lobes with the cerebellum, and roofing over the 

 anterior part of the fourth ventricle. It lies 

 beneath the anterior part of the cerebellum, 

 which must be gently pressed backwards to 

 expose it. 

 ii. The velum medullse posterius is a thin trans- 

 parent membrane, forming the roof of the pos- 

 terior part of the fourth ventricle : it is covered 

 in front by the cerebellum. 



g. The pineal body is a small rounded median body, 

 lying on the optic lobes, and connected by a 

 stalk with the roof of the thalamencephalon. 



It is visible on the dorsal surface, in the angle 

 between the hinder ends of the cerebral hemi- 

 spheres and the cerebellum, but is very liable 

 to be torn away with the dura mater. It has 

 recently been shown to be a degenerate eye. 



2. The ventral surface of the brain. 



a. The cerebral hemispheres, as seen from below, are 



closely apposed in front, but diverge posteriorly. 

 About the middle of its length the inner 

 border of each hemisphere presents a notch, 

 which is continued outwards across the surface 

 of the hemisphere as a shallow groove, the 

 Sylvian fissure, separating the frontal lobe from 

 the temporal. 



b. The olfactory lobes lie, in their hinder portions, 



along the under surface of the frontal lobes of 

 the hemispheres, extending back as far as the 

 Sylvian fissures. In front, they project some 

 distance beyond the hemispheres. 



c. The infundibulum is a median rounded elevation, 



lying between the temporal lobes, about the 

 middle of the length of the brain : at its apex is 

 the rounded vascular pituitary body. This latter 

 is usually left behind in the pituitary fossa in 



