BRAIN OF MAN. 369 



from each, other by the division of the broad fibrous band^J 

 termed the corpus callosum, which unites them. Each, hemi- 

 sphere is considered as made up of three lobes or divisions, 



7 11 9 10 6 e 



Fig. 106. SECTION OF THE BRAIN op MAN. 



the anterior a, the middle 6, and the posterior c; but these 

 are not by any means distinctly marked-out, either on the 

 external surface or in the internal structure of the organ. The 

 vesicular or ganglionic nerve-substance is disposed for the 

 most part upon the exterior, forming a continuous layer, whose 

 extent is greatly increased by the convoluted folds in which it 

 lies ; and it is very copiously supplied with blood from the 

 pia mater, a membrane which consists almost entirely of blood- 

 vessels and of the areolar tissue that holds them together, and 

 which so closely enfolds the hemispheres as to dip down into all 

 the furrows of their surface. The principal part of the internal 

 substance of each hemisphere is composed of nerve-fibres, of 

 which some pass between its convolutions and the chain of 

 ganglionic masses on which the cerebrum is superposed, others 



B B 



