MEDULLA SPINALIS. 



99 



Fig. 25^ 



posed, however, that they are all fused into one common trunks for 

 each individual filament of every nerve runs a separate and distinct 

 course from its starting point to its termination. It will hence be 

 understood, that it is the ivliiie or fibrous matter of the cord that is 

 connected with the cerebro-spinal division, and which is concerned in 

 sensation and voluntary 'motion^ or in other words, in the transmis- 

 sion of nervous influence to atidfrom the brain. 



The spinal cord is traversed by an anterior and a posterior 

 fissure dividing it into tivo lateral halves^ each of these also is 

 marked by two furrows on each side, subdividing it into three 

 columns. There are, therefore, upon each half of the cord, an an- . 

 terior^ middle or lateral, and posterior column. Each spinal nerve 

 arises by two roots, an anterior and a posterior. The anterior root 

 joins the spinal cord near the anterior furrow, and the posterior 

 near the posterior furrow. (Fig. 25.) 



The functions of these 

 two roots are now esta- 

 blished. The posterior., 

 which is distinguished by 

 having a ganglion upon 

 it, is the afferent root. 

 Part of its fibres run on 

 to the brain, conveying 

 impressions to this organ ; 

 part terminate in the gray 

 matter of the spinal cord, 

 in like manner convey- 

 ing impressions to the 

 latter. In a word, the 

 posterior root is the sen- 

 sory root. 



The anterior is the 

 efferent or motor root. Part of its fibres come from the brain con- 

 veying voluntary motion ; part have their origin in the gray matter 

 of the spinal cord, and are conveyors of excited motion from that 

 centre. Those fibres of both roots which are unconneicted with the 

 brain, constitute the system to which reflex actions are due, and with 

 the gray matter of the spinal cord, constitute a distinct nervous 

 circle. Each spinal nerve, then, contains at least four sets of fibres, 



I. A sensory bundle, passing upwards to the brain. 



II. A motor set, conveying the influence of volition and emotion 

 down wards y>-o?7Z the brain. 



* Transverse section of human spinal cord, close to the third and fourth cervical nerves. 

 / Posterior columns, i i. Gelatinous substance of the posterior horn. k. Posterior root. 

 /. Supposed anterior root. a. Anterior fissure, c. Posterior fissure, g. Anterior horn of 

 gray matter, e. Antero lateral column, (from k to o.) 



