98 THE SPINAL CORD AND CEREBELLUM 



large, and those passing to the muscles and sensory 

 surface of the trunk being proportionately smaller. 

 These conditions are reflected in the cord itself, and 

 especially in the size of the gray matter, which in the 

 lower cervical or neck portion — whence the nerves of 

 the arms proceed — and in the lower lumbar and sacral 

 portion — whence the nerves to the leg issue — is very 

 considerable, whilst in the intervening dorsal region 

 its dimensions shrink to one-half or one-third of 

 the extent occupied by it in the localities just 

 mentioned. 

 mttter*'' '^^^ 8^^^ matter is divided into a so-called anterior 

 or ventral and posterior or dorsal horn, to which a 

 lateral horn is sometimes added, and comprises several 

 groups of cells which increase, diminish, or disappear 

 as one passes up or down the cord. Thus, there are 

 median, central, ventro - lateral, and dorso - lateral 

 groups. Most of the cells of the ventral horn are 

 supposed to send fibres into the anterior roots of the 

 spinal nerves,* the impulses passing along them being 

 motor either to the muscles or to the bloodvessels of 

 the body and limbs. The dorsal horn is composed to 

 a great extent of masses of intersecting fibres termed 

 the lateral and posterior formations. There is, how- 

 ever, in addition an important group of cells called 

 the vesicular cylinder or Clarke's column. It extends 

 from the eighth cervical to the third lumbar nerve, at 

 which points it is interrupted, reappearing, however, 

 between the second and third cervical nerves, and 

 * Foster, loo. ait., p. 936. 



