404 



HUMAN PHYSIOLOGY 



The Brain of Man. — In man, as in the frog, the central nervous 

 system consists of a brain and spinal cord inclosed in a bony case 

 with the nerves leaving^ it. From the brain, twelve pairs of nerves 

 are given off; thirty-one more leave the spinal cord. Along the 

 course of some of these nerves are found ganglia. The brain has 

 three divisions. The cerebrum makes up the largest part. In this 

 respect it differs from the cerebrum of the frog and other verte- 

 brates. It is divided into two lobes, the hemispheres, which are 

 connected with each other by a broad band of nerve fibers. The 



Cerebrum 



Cerebellum — 



Medulla 



The brain, with parts separated to show each clearly. 



outer surface of the cerebrum is thrown into folds or convolutions. 

 The outer layer, seen in section, is gray in color, made up of nerve 

 cells and supporting material (the neuroglia, a kind of connective 

 tissue). The inner part (white in color) is composed largely of 

 fibers which pass to other parts of the brain and down into the 

 spinal cord. (In man, the midbrain is covered by the cerebrum, 

 and need not be considered in this description.) Under the 

 cerebrum, and dorsal to it, lies the little brain, or cerebellum, a 

 part of the hindbrain. This part consists of nerve cells and fibers. 

 The two sides of the cerebellum are connected by a band of nerve 



