Chap. XIX] 



THE NERVOUS SYSTEM 



389 



close relation to intellectual power ; babies and idiots have few 

 and shallow folds, while the brains of men of intellect are always 

 markedly convoluted. There are five important fissures which are 

 always present. They are the following : — 



(1) The Great Longitudinal Fissure, which extends from the 

 back to the front of the cerebrum, and almost completely divides 

 it into two hemispheres, the two halves, however, being connected 

 in the centre by a broad, transverse band of white fibres called the 

 corpus callosum. A process of the dura mater extends down into 

 this fissure and separates the two cerebral hemispheres. It is called 

 the falx cerebri, because it is narrow in front, and broader behind, 



Fig. 185. — External View of Outer Side of Right Cerebral Hemi- 

 sphere, SHOWING Rolando, Sylvian, and Parieto-occipital Fissures to- 

 gether with Principal Convolutions. (Collins.) 



thus resembling a sickle in shape. In a previous chapter it was 

 stated that the blood was returned from the brain in venous chan- 

 nels called sinuses. Two important sinuses are lodged between 

 the layers of the falx cerebri. The superior longitudinal sinus is 

 contained in the upper border, and the inferior longitudinal sinus 

 in the lower border. 



(2) The Transverse Fissure, which is between the cerebrum and 

 the cerebellum. A process of the dura also extends into this fis- 

 sure, and covers the upper surface of the cerebellum and the 

 under surface of the cerebrum. It is called the tentorium cerehelli. 



