The spino-thalamic, spino-tectal and ventral spino-cerebellar fasciculi form one compound funiculus from the spinal cord up to the middle of the pons; this is the tract of Gowers, first de scribed in 1897. At the level of the root of the trigeiminal nerve it divides into a bundle going to the cerebellum and parts going to the tectum (both colliculi) and to the thalamus.
3. The spino-thalamic tract occupies the lateral part of the formatio reticularis where it forms a loose strand (Figs. 113-118). As already stated, it rises in the spinal cord from the basal gray substance of the anterior columna and from the terminal nuclei of common sensory cerebral nerves in the medulla and pons. The spino-thalamic tract ends in the lateral nucleus of the thalamus. It conducts impulses of the tactile, pain and temperature senses.
4. Those fibers of Gower's tract that end in the inferior and superior colliculi of the tectum constitute the spino tectal fasciculus. It probably carries tactile pain and tem perature impulses which, however, do not excite the correspond ing sensations, but set up the proper reflexes in the tectum.
5. The ventral fasciculus is the third bundle of Gowers' tract. Like other parts of Gowers' tract, it rises from the basal part of the anterior column of gray substance in the cord and from terminal nuclei of common sensory cranial nerves. The ventral spino-cerebellar fasciculus terminates in the cortex of the superior vermis, largely on the opposite side. It accompanies the spino-thalamic tract as far as the root of the trigeminal nerve; bending backward at that level, it winds over the dorso-lateral surface of the brachium conjunctivum and continues through .the superior medullary velum to the vermis.
A small strand of large fibers diverges from the ventral spino-cerebellar fasciculus in the pons, and enters the cerebellum through the caudal half of the brachium pontis; it terminates also in the anterior cortex of the•. superior vermis. This bundle has been described by G. B. Pellizzi as an intermediate spino-cerebellar fasciculus, because in the cord ascends be tween the ventral and dorsal fasciculi.
The ventral spino-cerebellar tract probably carries tactile, pain and temperature impulses for the purpose of exciting reflex coordinating impulses in the cerebellum; but these impulses may reach the centers of consciousness and evoke their proper sensations. The tract thus belongs to the in
direct sensory path (through the cerebellum). From the cerebellar cortex the path is continued by the axones of Purk inje's cells to the nucleus dentatus, whence the brachium con junctivum completes it up to the opposite red nucleus and thalamus. The ventral spino-cerebellar and the spino-thalamic and spino-tectal tracts are the chief bundles of a spino-en cephalic system of fibers which terminates very largely in the cerebellum, tectum and thalamus, but also sends fibers to the nucleus lateralis inferior and other reticular nuclei, to the substantia nigra, to the nucleus ruber, the nucleus hypo thalamicus, and the corpus striatum.
6. The medial (posterior) longitudinal bundle (fasciculus longitudinalis medialis) (Figs. 113-118) runs next the median plane and just under the ventricular gray matter in a position similar to the one it occupies in the mid-brain (Figs. 59 and 6o), see p. 152. It is in the pontine portion of this bundle that the fibers from the oculomotor nucleus pass to the genu of the facial nerve, ultimately to innervate the frontalis, corrugator and orbicularis oculi; it is in the pons that fibers from the abducent nucleus join this bundle and run upward through it to the oculomotor nucleus of the opposite side and make pos sible the conjugate movements of the eyeballs; it is also here that fibers which rise in the hypoglossal nucleus leave the longitudinal bundle and enter the facial nerve at the genu to be distributed by way of the facial to the orbicularis oris. As in the mid-brain the longitudinal bundle includes the two functional tracts, the descending strand and the ascending strand.
Such connections as are described above are claimed by Duval and Laborde, and by Mendel, and they afford explana tions of well-known phenomena; but no one has actually traced these fibers either by myelenization or degeneration. On the other hand, Harman claims that the nerve supply of the facial muscles above the orbit is derived from the superior part of the facial nucleus; and the nucleus of the facial nerve innervates all the facial muscles, according to G. Elliot Smith. Further more, Schafer and Swimington, and E. H. Fraser deny the existence of fibers running from the abducent nucleus to the nucleus of the oculomotor nerve on the opposite side.