Anterior Tecto-spinal Bundle (Figs. 142 and r43).—Held called it the fasciculus longitudinalis ventralis. It occupies a very narrow strip in the anterior column just beside the en trance of the anterior median fissure. The anterior tecto spinal bundle has already been traced from its origin in the superior quadrigeminal colliculus, through the dorsal tegmented decussation (Meynerti) to a position in the mid-brain ventro lateral from the medial longitudinal bundle. It descends in that relative position through the pons and half the medulla; near the pyramidal decussation the anterior and medial longitudinal bundles are brought together and lie between that decussation and the isolated head of the anterior columna; they diverge upon entering the cord and remain separate to the end. The anterior tecto-spinal fasciculus ends in both anterior column (Collier). It forms the middle link in the ocular and pupillary reflex arcs.
The tract (fasciculus vestibulo-spinalis) rises in the lateral vestibular nucleus (of Deiters) and terminates in the gray matter of the cord. The vestibulo-spinal tract, in section, forms a crescentic zone of the cord reaching from the anterior pyramidal tract outward and backward, over the antero-lateral fasciculus proprius, to the middle of the lateral column. It is divided by the anterior roots of the spinal nerves into an anterior and a lateral fasciculus. The lateral vestibulo-spinal tract is intermediate in position between the fasciculus proprius and Gowers' tract, the latter separates it from the surface of the cord. It is more or less intermingled with the rubro-spinal, thalamo-spinal, lateral tecto-spinal and lateral reticulo-spinal tracts, though the former two run largely dorsal to it. The anterior vestibulo-spinal tract is blended superficially with the anterior fibers of the spino-thalamic tract and deeply with fibers to and from the reticular formation. The vestibulo-spinal tract joins the vestibular nerve directly with the motor spinal nerves. It also forms a descending link in the cerebellar arc of equilibrium; the other descending links of the arc are the cortico-nuclear fibers of Purkinje's cells, going to the nucleus fastigii; and the fastigio-bulbar fibers which end in the nucleus of Deiters. The vestibulo-spinal tract presides over muscle tone, coordination and equilibrium.
In the ventral portion of the lateral vestibulo-spinal tract, the lateral reticulo-spinal tract descends from the opposite nuclei of the reticular formation in the brain-stem; and, be hind that, descends the lateral tecto-spinal tract, which rises in the tectum on the same side, chiefly in the superior colliculus.
Both tracts terminate in the gray matter of the cord, probably in the anterior columna. Dorsal to the vestibulo-spinal tract, and blended with it to some extent, run the rubro-spinal and thalamo-spinal tracts to be described below: they separate the vestibulo-spinal tract from the lateral pyramidal tract.
Gowers' Tract.—This is a compound funiculus composed of several fasciculi. It forms the antero-lateral surface of the cord from a line midway between the posterior and anterior roots of the spinal nerves forward almost to the anterior pyrami dal tract. Behind, it is in contact with the dorsal spino cerebellar tract. It intermingles with the spino-olivary tract just lateral to the anterior nerve-roots, and with the vestibulo spinal tract medial to those roots. Gowers' tract, though it possesses many terminations, has one common origin from the basal region of the anterior columna in both crescents. Some writers claim that Gowers' tract rises from the base of the posterior columna, especially from the dorsal nucleus of Clark; and there is evidence that a number of fibers from the dorsal nucleus do ascend within it for a short distance, hut they soon trend backward into the dorsal spino-cerebellar fasciculus. The larger number of fibers in Gowers' tract rise in the opposite anterior columna and cross over through the white commissure; the uncrossed fibers rise in relation with axones that cross through the gray commissure from cell-bodies in the opposite crescent, so the conduction path to which the tract belongs is wholly a crossed one. The tract of Gowers runs as one com pact funiculus through the spinal cord. In the brain-stem, it separates into several fasciculi which terminate in the reticular nuclei, the cerebellar cortex, the tectum, the substantia nigra, the thalamus, etc. Four of these fasciculi are commonly distinguished by specific names; the spino-reticular, spino tectal, ventral spino-cerebellar, and spino-thalamic. The two latter are the more important. The spino-reticular fasciculus ends in the nuclei of the reticular formation, chiefly in the in ferior lateral nucleus of the medulla; and the reticulo-cerebellar tract continues its conduction to cerebellar cortex. The spino tectal fasciculus terminates in the superior and inferior quad rigeminal colliculi of the tectum. It forms a link in a reflex arc.