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White Matter of the Cord

anterior, fibers, gray, tracts, spinal and commissure

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WHITE MATTER OF THE CORD The white matter (Fig. 140) of the spinal cord (substantia alba spinalis) is disposed in its peripheral area and in the white ante rior commissure. It is composed of medullated nerve fibers (axones and collaterals) imbedded in a small amount of neu roglia, and supported by a connective tissue network derived from the pia mater. Like the gray matter it is richly supplied with blood-vessels. The fibers of the spinal cord run trans versely, dorso-ventrally and longitudinally.

The transverse fibers, which are usually somewhat oblique in direction, comprise (r) those running from the longitudinal tracts into the gray matter or out of the gray matter into such tracts; (2) the axones of intrinsic neurones which run through the gray commissure and connect the two crescents at nearly the same level; and (3) the fibers of the white commissure.

The transverse fibers of the gray commissure are derived from cell-bodies located in the posterior columna in relation with in coming root-fibers, and in the center of the crescent. As they pass over to the opposite crescent, they are massed along the dorsal and ventral surfaces of the central gelatinous substance, in the posterior and anterior gray commissures. The fibers of the gray commissures radiate in the anterior columna and center of the crescent and form contacts with intrinsic neurones of those parts.

The white anterior commissure of the spinal cord (commissura anterior alba) is the most definite lamina of transverse fibers in the cord (Fig. 139). It connects the anterior and lateral white columns of the cord with the opposite gray crescent and the two crescents with each other. It is located in front of the gray anterior commissure, forming the floor of the anterior median fissure. It is composed of medullated fibers belonging to (a) the anterior pyramidal tract; (b) the anterior fasciculus pro prius; (c) the ventral spino-cerebellar and spino-thalamic tracts; (d) it comprises the crossed fibers to the anterior roots of the spinal nerves, and (e) the decussating dendrites between the anterior columne.

The dorso-ventral fibers of the spinal cord (Fig. 145) are (a) those of the anterior roots of the spinal nerves, in their course from the gray matter to the surface of the cord; (b) those of the posterior roots, running from the posterior-lateral sulcus to their destination in the gray matter, and (c) axones of intrinsic neu rones connecting posterior with anterior parts of the crescent.

The longitudinal fibers comprise most of the white matter in the cord, forming the funiculus anterior, funiculus lateralis and funiculus posterior (Figs. 139 and 140). These three great columns occupy the anterior, lateral and posterior areas of the cord. They are disposed around the gray crescent in bundles or tracts. The tracts which make up the funiculi are not visible to the naked eye, nor under the microscope in a healthy adult cord; they have been located by embryological, experimental and pathological investigations. The longitudinal fibers rise in the brain, in the spinal cord and in the spinal ganglia; some run upward and others downward, constituting the tracts of the cord. Thus the tracts are characterized as ascending, descend ing and mixed tracts. The mixed tracts are the fasciculi proprii. They are made up of T-branched axones and present about an equal intermingling of ascending and descend ing fibers. The simple fasciculi or tracts are so named as to indicate the direction of their growth and conduction: the first element of the compound noun indicates the origin, the second element designates the termination of the tract. The tracts of the cord are as follows: Funiculus Anterior.

Fasciculus proprius anterior, with fasc. longitudinalis medialis.

Tractus pyramidalis anterior or fasc. cerebrospinalis anterior.

Fasciculus tecto-spinalis anterior.

Fasciculus reticulo-spinalis anterior.

Funiculus Lateralis.— Fasciculus proprius lateralis with Cajal's bundle of the dorsal horn.

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