THE BRAIN. 123 



sure of Sylvius, divides each hemisphere obliquely into two 

 lobes, the anterior and posterior. 



The surface of the hemispheres is broken with deep irregular 

 suld or furrows, which define the oblong rounded winding 

 ridges, themselves subdivided by secondary furrows, and 

 called, from their analogy to the windings of the smaller 



Fig. 31. Upper surface of the brain. 

 A, A. Great fissure. B, B. Cerebral hemispheres. 



intestine, the convolutions of the brain. Some of these are 

 always present, and appear symmetrically in both hemi- 

 spheres; others are variable, not found on both sides, differing 

 in length, breadth, and in projection. These convolutions 

 cover the external, superior, and inferior surfaces of both 

 hemispheres, and are continued also on their internal surface 

 the whole length of the great fissure, and of the fissure of 

 Sylvius. 



