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a section of the cord a rather oval outline_broader or narrower, according to location. From the center of the periphery anteriorly a slight cleft extends into the substance of the cord, reaching nearly to the anterior gray commissure, which is called the anterior median fissure. Opposite this a slight cleft occurs on the posterior aspect which is continued nearly to the posterior gray commissure as a fibrous line, known as the posterior median fissure. Between the bottom of the anterior and posterior median fissures and the gray commissure are small bridges of white substance, called respectively the anterior and the posterior white commissures. The two fissures and the horns of

gray

matter divide the cord into vertical columns, which have been termed the primary columns. The two masses of tissue on either side of the anterior median fissure and the anterior horns are called the anterior columns. That between the anterior and the posterior on the same side form the lateral columns. Both of the former taken together are sometimes known as the anterolateral columns. The white matter situated between the posterior fissure and the posterior horns is known as the posterior column.

Each of these columns is further subdivided into secondary columns, according to the distribution of the fibers composing it.

About half of the anterior columns (adjacent to the fissure) is composed of fibers running downward, and is called the direct pyramidal tract, or Türck's column.

The remainder of the anterior column is composed of fibers carrying ascending impulses, and constitutes the anterior ground bundle, or anterior fundamental column.

The lateral column is divided into five tracts—the

direct cerebellar, the ascending anterolateral or Gowers' tract, the crossed pyramidal, the descending anterolateral, and the mixed lateral.

The direct cerebellar tract occupies a narrow band at the posterior half of the surface of the lateral column. Its fibers are descending.

The crossed pyramidal tract lies internal to the direct cerebellar tract, its fibers being descending.

The descending anterior lateral tract lies internal to Gower’s tract and anterior to the crossed pyramidal tract. Its fibers are descending.

The mixed lateral tract occupies a small space bounded internally by the gray matter and externally by portions of both the crossed pyramidal and the descending anterolateral tract. The mixed tract contains both ascending and descending fibers.

The posterior column is divided into two tracts—the column of Burdach and the column of Goll.

The column of Goll, or fasciculus gracilis, occupies a wedge-shaped area covering the median half of the posterior column. Its fibers are ascending.

The column of Burdach, or fasciculus cuneatus, occupies the remainder or lateral half of the anterior column. Its fibers are also ascending.

MINUTE STRUCTURES. The gray substance consists of an intricate tangle of nerve-cells, nerve-fibers, and a specialized connective tissue, called the neuroglia.

The nerve-cells in the gray matter are arranged more or less in groups. In the anterior horns four groups may be recognized the inner or median, the anterior, the anterolateral, and the posterolateral. At about the junction of the anterior and posterior horns,

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