THE NERVOUS SYSTEM. 



145 



7, The spinal cord occupies the spinal canal in the 

 backbone. It is about half an inch thick, and eighteen 

 inches long. Before reaching the 



lower end of the canal, it divides > 

 into a bunch of fine cords, which * 

 make the cauda equina (horse's 

 tail). 1 



The spinal cord, like the brain, 

 is partly divided, lengthwise, into g j 

 two halves, which are alike. 



8, Both the brain and spinal 

 cord have three coverings wrapped | 

 around them, called the membranes * |j 

 of the brain and cord. 



From each half of the brain ^ 

 twelve small cords come off, and j* 

 go out through holes in the skull. ~ 

 From each half of the spinal cord * 

 thirty-one small cords come off, 

 by two roots each, and go out of 

 the spinal canal through openings 

 between the vertebrae. These are I 

 the nerves. 



9, The substance of the brain 

 and cord is soft and cheese-like, g 

 It is of two colors, white and gray. 



The whole surface of the cerebrum and cerebellum, about 

 a quarter of an inch deep, is gray. The deep parts of both 

 are chiefly white. In the cord, it is different. The deep 

 part is gray, and the surface is white. 



10, A blow on that part of the elbow called the "funny- 

 bone," gives a tingling sensation all the way down to the 

 little finger. 



