THE BEAIN 341 



A. The Brain-membranes, 



1. The dura mater is the tough connective-tissue membrane 



which lines the cranial cavity. The greater part or 

 the whole of it is left in the skull on removal of the 

 brain. It projects into the cranial cavity as a median 

 vertical fold, the falx cerebri, which lies between 

 the nemispheres ; 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 

 appcfeed 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. 



