144 THE HUMAN BODY 



C, shows also that the substance of the cord is not alike through- 

 out, but thai its white superficial layers envelop a central gray 

 substance arranged somewhat in the form of a capital H. Each 

 half of the gray matter is crescent-shaped, and the crescents are 

 turned back to back and united across the middle line by the 

 gray commissure. The tips of each crescent are called its horns or 

 cornua, and the ventral horn on each side is thicker and larger 

 than the dorsal. In the cervical and lumbar enlargements the 

 proportion of white to gray matter is greater than elsewhere; and 

 as the cord approaches the medulla oblongata its central gray 

 mass becomes irregular in form and begins to break up into smaller 



FIG. 58. Diagram illustrating the general relationships of the parts of the brain. 



A, fore-brain; b, midbrain; B, cerebellum; C, pons Varolii; D, medulla oblongata; 



B, C, and D together constitute the hind-brain. 



portions. If lines be drawn on the transverse section of the cord 

 from the tip of each horn of the gray matter to the nearest point 

 of the surface, the white substance in each half will be divided into 

 three portions: one between the ventral fissure and the ventral 

 cornu, and called the ventral white column; one between the dorsal 

 fissure and the dorsal cornu, and called the dorsal white column; 

 while the remaining one lying in the hollow of the crescent and 

 between the two horns is the lateral column: the ventral and lateral 

 columns of the same side are frequently named the ventrolateral 

 column. A certain amount of white substance crosses the middle 



