352 DISSECTION OF THE RABBIT 



vertical fold, the falx cerebri, -which lies between 

 the hemispheres ; and a transverse fold, the tento- 

 rium, which separates the hemispheres from the 

 cerebellum. 

 2. The pia mater is a much thinner and very vascular 

 layer of connective tissue, which closely invests the 

 brain, and conveys blood-vessels to and from the 

 brain substance. 



B. External Characters of the Brain. 



Strip off the pia mater from the brain with fine forceps as 

 fully as possible, taking great care on the base of the brain 

 not to drag away the nerve-roots. 



1. The dorsal surface of the brain, 



a. The cerebral hemispheres, which form the anterior 



two-thirds of the brain, are a pair of broad 

 triangular bodies, pointed in front and closely 

 apposed to each other along the median plane. 



Their surfaces are smooth and convex : they 

 are marked by a few shallow grooves, or sulci ; 

 and they are divided by rather more conspicuous 

 grooves at their outer edges into anterior or 

 frontal, and posterior or parietal lobes. 



The two hemispheres are connected with each 

 other by a large transverse commissure, the 

 corpus callosum, which is readily seen on gently 

 separating the hemispheres with the handle of a 

 scalpel. 



b. The olfactory lobes are a pair of large club-shaped 



bodies, projecting forwards from beneath the 

 anterior ends of the hemispheres. 



c. The thalamencephalon is covered by the hemi- 



spheres, and cannot be seen from the dorsal 

 surface. 



d. The corpora quadrigemina, or optic lobes, are t"wo 



pairs of rounded elevations on the dorsal surface 

 of the brain, and almost completely covered by 

 the hemispheres. 



