3 66 



ELEMENTAR Y ANA TOM Y. 



[LESS. 



The cerebro-spinal axis encloses a cavity (of very different 

 size and shape in different parts) which is lined by another 

 very delicate epithelial layer called the ependema. 



4. The BRAIN fills up the whole cranial cavity, fitting into 

 all those depressions which we have found to exist on the 

 floor of that cavity. 



On removing the upper part of the skull and the dura 

 mater, the surface of the brain is seen as a convex mass 

 covered with numerous meandering, contorted prominences 

 (convolutions or gyri), separated by corresponding depres- 

 sions (fissures or suld\ The whole mass is sharply divided 

 by a very deep fissure running from before backwards, and 

 dividing the visible part of the brain into two lateral halves, 



FIG. 323. THE UPPER SURFACE OF THE BRAIN OF MAN, showing the deep 

 longitudinal fissure dividing the two hemispheres, with their numerous and 

 unsymmetrical convolutions. 



termed hemisplicres, and the whole convoluted mass is called 

 the cerebrum. Thus the cerebral hemispheres of man extend 

 so far forwards, outwards, and backwards that no other part 

 of the cerebro-spinal axis is visible when the brain is viewed 

 from above The pia mater so closely invests this mass that 

 it passes down not only into the great median longitudinal 

 fissure, but into all the sulci of the cerebrum. The dura 

 mater passes into the longitudinal fissure only, where it forms 

 the falx, which, as we have found in some a.iimals (e.g. the 

 Ornithorhynchus), becomes ossified. 



Upon pushing apart the two cerebral hemispheres, these 

 are seen to be connected by a large transverse band (called 



