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 —Different views of a portion of the spinal cord from the cervical region, with the roots of the nerves. In A the anterior surface of the specimen is shown, the anterior nerve root of its right side being divided; in B a view of the right side is given; in C the upper surface is shown; in D the nerve roots and ganglion are shown from below: 1, the anterior median fissure; 2, posterior median fissure; 3, anterior lateral depression, over which the anterior nerve roots are seen to spread; 4, posterior lateral groove, into which the posterior roots are seen to sink; 5, anterior roots passing the ganglion; 5´, in A, the anterior root divided; 6, the posterior roots, the fibers of which pass into the ganglion, 6; 7, the united or compound nerve; 7´, the posterior primary branch seen in A and D to be derived in part from the anterior and in part from the posterior root. (Allen Thomson.)

most important are the anterior and posterior median, the latter being rather a dividing line or septum. By them it is divided into halves connected by a small band in the middle called the commissure. The white matter is exterior to the gray and is divided by it into four columns, which again are divided into tracts according to certain groups of nerves that travel through them. The most important tract is the direct pyramidal tract in the anterior column. The gray matter is arranged in the form of a letter H practically, consisting of two lateral halves, more or less crescentic in outline, connected by a narrow band, the gray commissure. Each half is divided into two horns, the anterior, toward the front of the cord, and the posterior, toward the back, the former being generally much thicker and heavier than the latter. The structure of the gray and
 * cular and is divided by certain fissures, of which the