788 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



central canal, which passes from the floor of the fourth ventricle 

 downward and is lined by a layer of cylindrical epithelial cells. 



The cells of the gray matter of the spinal cord differ greatly in size, 

 those in the anterior horn being much the largest. The gray matter is, 

 also, like the white matter, arranged in columns, although the distinc- 

 tion between these columns may be less readily demonstrated. Thus, 

 the anterior and posterior horns form the anterior and posterior gray 

 columns, while between the two lies the lateral column. 



The distribution of white and gray matter varies in shape in differ- 

 ent portions of the spinal cord. In the cervical region the lateral white 

 columns are large, the anterior horn of the gray matter is wide and 



I 



Fig. 334.— Transverse Section of the Spinal Cord in the Lumbar 

 Region, after Sevan Lewis. ( Yco.) 



(For references see description under Fig. 333.) 



large, while the posterior horn is narrow and the transverse diameter of 

 the cord is the longest (Figs. 333, 334 and 335). In the dorsal region both 

 cornua are narrow and of nearly equal breadth, while the cord is smaller 

 and cylindrical. 



In the lumbar region the gray matter is largest in amount, while the 

 lateral columns are small and the central canal is nearly in the middle of 

 the cord. 



As a rule, the anterior horn of grajr matter is shorter and broader, 

 and does not extend so near to the surface of the cord as does the pos- 

 terior horn, which is more pointed, longer, and narrower, and usually 

 extends nearer to the surface. 



