THE SPINAL CORD. 451 



dorsal surfaces are known as the ventral and dorsal roots. The ventral 

 roots are the axons of various groups of cells in the anterior horns. 

 From their origin these axons pass almost horizontally forward 

 through the anterior column in three distinct bundles. After emerging 

 from the cord they curve downward and backward to join the poste- 

 rior root. The dorsal roots are the central axons of nerve-cells in the 

 spinal ganglia. After entering the cord they divide into two main 

 groups, a lateral and a mesial. A portion of the lateral group enters 

 the posterior horn directly through the caput cornu ; the other portion 

 turns upward and runs through Lissauer's tract and ultimately enters 

 the posterior horn. The mesial group passes into the postero- 

 external column (Burdach), where the fibers divide into descending 

 and ascending branches. The former constitute the comma tract, 

 the terminal branches of which surround cells in the gray matter; 

 the latter (ascending) cross the column obliquely and enter the 

 postero-internal column (Goll), in which they pass upward to ter- 

 minate around the cells of the nucleus gracilis of the same side. As 

 these root fibers pass up and down the cord, collateral branches are 

 given of! which enter the gray matter at successive levels and come %L y 

 into physiologic relation with the cells of Clark's vesicular column 

 on the same and opposite sides and with the cells of the anterior horn. 



Experimentally, it has been determined that the anterigjjjjyyjen- 

 tral roots cotjj^u^jyjjetfjjgjgjjyfijjjgr^ the posterior or dorsal roots 

 all the afferent fibers. Tn^mxrt^n support of this view are 

 follows: 



Stimulation of the ventral roots produces : 



1. Convulsive movements of muscles. 



2. The discharge of a secretion from glands. 



3. Changes in the caliber of blood-vessels. 



4. Inhibition of the rhythmic activity of certain organs. 



Division of these roots is followed by: 



1. Loss of muscle movement (paralysis of motion). 



2. Cessation of normal secretion. 



3. Cessation of active vascular changes. 

 Stimulation of the dorsal roots causes : 



1. Reflex activities. 



2. Conscious sensations. 



3. Inhibition of the rhythmic activity of certain organs. 

 Division of these roots is followed by: 



1 . Loss of reflex activities, and 



2. Loss of sensation in all parts to which they are distributed. 



A The ventral roots are, therefore, efferent in function, transmitting 1 

 nerve impulses from the nerve centers to the periphery. They 

 *V dorsal roots are afferent in function, transmitting nerve impulses fron/ 

 the general periphery to the nerve centers. 



