CHAPTER XXI 

 THE BRAIN AND CRANIAL NERVES 



The cerebro-spinal or central nerve system comprises the 

 Brain and Spinal Cord with their nerves. The spinal cord and 

 its nerves are already described in Chapters XIX and XX. 



The brain 1 is ovoid in shape, composed of gray cells and white 

 fibers, situated within the cranial cavity and continuous through 

 the foramen magnum with the spinal cord. 



FIG. 191. THE EXTERNAL SURFACE OF THE BRAIN. (Deaver.) 



The surface consists of gray cells and their branches and is 

 called the cortex of the brain, while the interior is white, with several 

 ganglia imbedded within it. 



The surface or cortex of a well-developed brain is marked by 

 many fissures, separating curved ridges called convolutions (or 

 gyres), the number and depth of which correspond with the degree 

 of development, the brain of a new-born child being comparatively 

 smooth. 



1 A review of pages 277 and 278 is recommended before studying the description 

 of the brain. 



299 



