SPINAL CORD. 



117 



by the anterior and posterior fissures. It is composed of both white or 

 fibrous and gray or vesicular matter, the former occupying the exterior of 

 the cord, the latter the interior, where it is arranged in the form of two 

 crescents, one in each lateral half, united together by the central mass, the 

 gray commissure ; the white matter being united in front by the white 

 commissure. 



Structure of the White Matter. The white matter surrounding each 

 lateral half of the cord is made up of nerve fibres, some of which are con- 

 tinuations of the nerves which enter the cord, while others are derived 

 from different sources. It is subdivided into: (i) An Anterior column, 

 comprising that portion between the anterior roots and the anterior fissure, 

 which is again subdivided into two parts : (#) an inner portion, bordering 

 the anterior median fissure, the direct pyramidal tract, or column of Turck, 

 containing motor fibres which do not decussate, and which extends as far 

 down as the middle of the dorsal region ; () an outer portion, surrounding 

 the anterior cornua, known as the anterior root zone, composed of short 

 longitudinal fibres which serve to connect together different segments of 

 the spinal cord. (2) A Lateral 

 column, the portion between 

 the anterior and posterior roots, 

 which is divisible into (a) the 

 crossed pyramidal tract, occupy- 

 ing the posterior portion of the 

 lateral column, and containing 

 all those fibres of the motor tract 

 which have decussated at the 

 medulla oblongata ; it is com- 

 posed of longitudinally running 

 fibres which are connected with 

 the multipolar nerve cells of the 

 anterior cornua ; (b} the direct 

 cerebellar tract, situated upon 

 the surface of the lateral column, 

 consisting of longitudinal fibres 

 which terminate in the cere- 

 bellum ; it first appears in the 

 lumbar region, and increases as 

 it passes upward ; (c] the anterior tract, lying just posterior to the anterior 

 cornua. (3) A Posterior column, the portion included between the posterior 

 roots and the posterior fissure, also divisible into two portions, (a) an inner 



SCHEME OF THE CONDUCTING PATHS IN THE 

 SPINAL CORD AT THE 3D DORSAL NERVE. 



The black part is the gray matter, v, anterior, 

 hw, posterior, root ; a, direct, and g, crossed, 

 pyramidal tracts ; b, anterior column, ground 

 bundle ; c, Coil's column ; d, postero-exter- 

 nal column ; e and f, mixed lateral paths ; h, 

 direct cerebellar tracts. Landois. 



