FUNCTIONS OF SPINAL CORD. 43 



Functions of the Spinal Cord. The spinal cord has 

 two main functions : 



1. Its Conducting Power, by means of the white fibers 

 which make up the outer part of the cord. These fibers may 

 be regarded as connecting the gray matter of the brain with 

 all parts of the body. 



2. The gray matter is the Center of the Reflex Actions of 

 the cord. 



In looking at the cross-section of the spinal cord, we see 

 that the dorsal and ventral grooves separate it into right and 

 left halves, connected by a comparatively narrow isthmus. 

 In this narrow part are fibers connecting the two halves. 

 The brain also consists of right and left hemispheres con- 

 nected by white fibers. Now, the gray matter of the outside 

 of the cerebral hemispheres is considered the chief seat of 

 both sensation and voluntary motion. 



Further, most of the fibers which connect this gray matter 

 of the cerebral convolutions, cross over to the other half of 

 the spinal cord on their way to that part of the body with 

 which they connect. Thus, when we wish to move the right 

 hand the action starts with certain changes taking place in 

 certain cells of the gray matter of the left cerebral hemi- 

 sphere. Certain fibers extend from these cells down to the 

 base of the brain, cross in the spinal bulb to the other half of 

 the spinal cord, and run down in the right half of the spinal 

 cord to the nerve leading to the muscles to be controlled. 



Similarly, the sensory nerves cross on their way to the 

 brain, only they are believed to cross soon after they enter 

 the spinal cord. For instance, the fingers of the right hand 

 touch an object. The nerve impulse thus started runs up 

 the afferent fibers of the nerve of the arm. As it reaches the 

 spinal cord it passes along the fibers of the dorsal root, and 

 enters the dorsal part of the cord. It then crosses, prob- 



