SPINAL CORD. 



183 



a 



of the spinal nerves, and are supposed to be motor in function. The 

 second group is situated in the posterior horn, the cells of which are 

 spindle-shaped, and from their relation to the posterior roots are 

 supposed to be sensory in function. The third group is situated in 

 the lateral aspect of the gray 

 matter, and is quite separate 

 and distinct, except in the 

 lumbar and cervical enlarge- 

 ments, where it blends with 

 those of the anterior horn. 

 A fourth group is situated 

 at the inner base of the pos- 

 terior horn ; it begins about 

 the seventh or eighth cervical 

 nerve and extends downward 

 to the second or third lum- 

 bar, being most prominent 

 in the dorsal region. This 

 column is known as Clark's 

 vesicular column. 



hw 



FIG. 21. SCHEME OF THE CONDUCTING 

 PATH IN THE SPINAL CORD AT THE 

 THIRD DORSAL NERVE. (Landois.) 



The black part is the gray matter, v. An- 

 terior, hw, posterior, root. a. Direct, 

 and g, g, crossed, pyramidal tracts. 



b. Anterior column, ground bundle. 



c. Coil's column, d. Postero-external 

 column, e, e, and f, f. Mixed lateral 

 p^ths. h, h. Direct cerebellar tracts. 



Structure of the White 

 Matter. The white matter 

 surrounding each lateral half 

 of the cord is made up of 

 nerve fibers, some of which are continuations of the nerves which 

 enter the cord, while others are derived from different sources. It 

 is subdivided into 



1. An anterior column, comprising that portion between the anterior 

 roots and the anterior fissure, which is again subdivided into two 

 parts : 



(a) An inner portion, bordering the anterior median fissure, 

 the direct pyramidal tract, or column of Tiirck ; it contains 

 motor fibers which do not decussate, and which extend as far 

 down as the middle of the dorsal region. 



(fr) An outer portion, surrounding the anterior cornua, known 

 as the anterior root zone, composed of short, longitudinal 

 fibers which serve to connect different segments of the spinal 

 cord. 



2. A lateral column, the portion between the -anterior and posterior 

 roots, which is divisible into 



