48 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



transverse plate. Tracing the fibers from the nerves, 

 we find that those from the posterior roots are seen to 

 enter the posterior horn of the gray matter; and those 

 of the anterior roots, into the anterior horn of the gray 

 matter (Fig. 31). The former enter, each, a sensory cell, 

 and through it communicates with a fiber going up the 

 posterior column toward the brain, and even, perhaps, 



Fig. 31. — r rosS section of half the 

 spinal cord, snowing how sensory 

 fibers, s, and motor fibers, m, 

 enter the gray matter. 



Fig. ?2. — Cross and longitudinal 

 section, showing how sensory 

 fibers, s, and motor fibers, m, 

 communicate with cells of gray 

 matter and pass on. Arrows 

 show direction of transmission. 



to the cerebral gray matter ; the latter similarly through 

 a motor cell and upward perhaps to the cerebrum. 

 This is shown in section (Fig. 32). 



Central Function. — The general function of the cord, 

 therefore, is twofold: first, it is a cable — the biggest 

 cable — of conducting fibers from the gray matter of 

 the brain to all parts of the body; and, second, it is 

 also a center of gray matter from which issue fibers to 

 all parts. As a center, its distinctive function is reflex 

 or automatic. It is called reflex because an impression 

 coming from a sensitive surface to this center is reflected 



