THE SPINAL CORD. 



497 



The intrinsic cells are associative in function. The axons to which these 

 cells give origin pass more or less horizontally into the white matter, where 

 they divide into two branches, one of which passes upward, the other down- 

 ward. At various levels they re-enter the gray matter and arborize around 

 other intrinsic cells. 



The efferent cells, independently of their trophic influence, are also motor 

 in function, inasmuch as the excitation arising in them is transmitted out- 

 wardly through their axons to muscles, glands, blood-vessels and viscera, 

 imparting to them motion, either molar or molecular. As the efferent 

 fibers in the ventral roots of the spinal nerves are classified (see page 97) 

 in accordance with their physiologic action into motor, secretor, vaso-motor, 

 viscero-motor and pilo-motor nerves, so the nerve-cells of which the nerves 



Dorsal 



FIG. 231. SCHEME OF THE STRUCTURE OF THE CORD. (Harwell after Lenhossek.) On the 

 right the nerve cells; on the left the entering nerve fibers. Right side: i, Motor cells, anterior 

 horn, giving rise to the fibers of the anterior root; 2, tract cells whose axons pass into the white 

 matter of the anterior and lateral columns; 3, commissural cells whose axons pass chiefly through 

 the anterior commissure to reach the anterior columns of the other side; 4, Golgi cells (second type), 

 whose axons do not leave the gray matter; 5, tract cells whose axons pass into the white matter 

 of the posterior column. Left side: i, Entering fibers of the posterior root, ending, from within 

 outward, as follows: Clarke's column, posterior horn of opposite side, anterior horn same side (re- 

 flex arc), lateral horn of same side, posterior horn of same side; 2, collaterals from fibers in the 

 anterior and lateral columns; 3, collaterals of descending pyramidal fibers ending around motor 

 cells in anterior horn. 



are integral parts may be classified physiologically as motor, vaso-motor, 

 secretor, viscero-motor and pilo-motor. Collections or groups of such cells 

 are termed "centers." 



The afferent cells are largely sentient or receptive in function, inasmuch 

 as the excitations brought to the spinal cord by the afferent nerves in the 

 dorsal roots from the general periphery are received by them and transmitted 

 by and through their axons to the cortex of the cerebrum, where they are 

 translated into conscious sensations. As the nerve- fibers in the dorsal roots 

 of the spinal nerves are classified, in accordance with the sensations to which 

 they give rise, as sensor, thermal, tactile, etc., so these nerve-cells may be 

 similarly classified according as they transmit their excitations to those 

 3 2 



