i66 



HUMAN PHYSIOLOGY. 



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 enlargements, where it blends with those 

 of the ventral horn. A fourth group is situated at the inner base of the 

 dorsal horn; it begins about the seventh or eighth cervical nerve and 

 extends downward to the second or third lumbar, being most prominent in 

 the dorsal region. This column is known as Clark's vesicular column. 



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 con- 

 tinuations for the nerves which enter 



l \, . the cord, while others are derived 



from different sources. It is sub- 



f \ x-TM/k t divWedinto - 



i. A ventral column, comprising that 

 portion between the ventral roots 

 and the ventral fissure, which is 

 again subdivided into two parts: 

 (a) An inner portion, bordering 

 the ventral 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. 



(6) An outer portion, surrounding 

 the ventral cornua, known as 

 the ventral 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 ventral and dorsal roots, which 

 is divisible into 



(a) The crossed pyramidal tract, occupying the dorsal portion of the 

 lateral column, and containing all those fibers of the motor tract 

 which have decussated at the medulla oblongata; it is composed of 

 longitudinally running fibers, which are connected with the multi- 

 polar nerve-cells of the ventral cornua. 



(6) The direct cerebellar tract, situated upon the surface of the lateral 

 column, consisting of longitudinal fibers which terminate in the 



FIG. 22. SCHEME OF THE CONDUCTING 

 PATH IN THE SPINAL CORD AT THE THIRD 

 DORSAL NERVE. (Landois.) 



The black part is the gray matter. v. 

 Ventral, hw, dorsal root. a. Direct, and 

 g, g, crossed, pyramidal tracts, b. Ven- 

 tral column, ground bundle. c. Coil's 

 column. d. Postero-external column, 

 e, e, and f, f. Mixed lateral paths. h, h. 

 Direct cerebellar tracts. 



