Nucleus Salivarius.—The salivary nucleus of Kohnstamm, mentioned in the description of the pons, is present almost wholly in the medulla. It is situated in the reticular substance of the lateral column, dorsal to the inferior olive. The lower part of this nucleus probably contributes the secretory and vasodilator fibers of the glossopharyngeal nerve, though it is possible that all the axones of the salivary nucleus enter the intermediate nerve (glosso-palatine nerve), as is suggested by Hardesty; they all terminate in sympathetic ganglia, especially in the spheno-palatine, otic and submaxillary and in smaller ganglia, as the sublingual, the parotid (of Schochet), etc.
The posterior columna is decapitated by the fillet. It is repre sented in the medulla (1) by the following terminal nuclei, viz., the sensory part of the nucleus alp cinerece of the vagus and glossopharyngeal nerves, the .vestibular and cochlear nuclei of the auditory nerve, the nucleus tractus solitarii and the nucleus of the spinal tract of the trigeminal nerve; and (2) by the gray matter of the reticular substance of the posterior column. All the posterior columna, except the dorsal nucleus of Clark, form somatic terminal nuclei (the trigeminal, vestibular and cochlear); the dorsal nucleus of Clark forms visceral terminal nuclei (the afferent part of the nucleus alp cinereee and the nucleus tractus solitarii).
The nucleus aloe cinerece of the vagus and glossopharyngeal nerves (Fig. .124) contains in its lateral part a group of small fusiform cell-bodies like those in the posterior columna. These fusiform cells constitute the terminal nucleus of the sensory fibers of the vagus, and it is probable that a few glossopharyn geal fibers also arborize and end in the nucleus. This is a visceral or splanchnic terminal nucleus. Cortical Connection.—Axones of this nucleus probably enter into the medial fillet, the spino thalamic tract, the restiform body and the medial longitudinal bundle. The two former conduct tactile, muscular, pain and temperature impulses to the thalamus, whence the cortical fillet carries them to the cortex; the latter establish its simple reflex connection, and, by way of the cerebellum and cerebello tegmental tracts, coordinated reflex connections. The intra nuncial connections are especially rich.
Solitarii (Figs. 123 and 125).—The nucleus of the solitary tract surrounds the tractus solitarius with which it coincides in extent. It is a special sense visceral nucleus, the gustatory nucleus of Nageotte. It is a part of the central
gelatinous gray substance and is situated just lateral to the nucleus of the ala cinerea. In its descent it trends dorsally and toward the median line. It is joined to the opposite nucleus at its spinal end by the nucleus commissuralis (Cajal). The nucleus of the solitary tract is the terminal nucleus of the afferent fibers of the intermediate and glossopharyngeal nerves and probably receives a few fibers from the vagus. It is thus the nucleus of the nerves of taste and forms the first relay station in the gustatory path. The axones of the cell-bodies in the nucleus tractus solitarii establish reflex connections with efferent nuclei and continue the taste path toward the thalamus.
Nucleus Tractus Spinalis Nervi Trigemini (Figs. 123 and 126). —The nucleus of the spinal tract of the trigeminal nerve is gelatinous in character. It is continuous with the sensory pon tine nucleus of the trigeminal nerve above and below is con tinued in the gelatinous substance of the posterior columna of the spinal cord. As low down as the second cervical segment it receives fibers from the trigeminal nerve so the terminal nucleus of this nerve extends from the middle of the pons to the second cervical nerve. It is a somatic terminal nucleus. The nucleus of the trigeminal is embraced between the emergent part of the facial nerve medially and the vestibular nerve laterally in the lower portion of the polls; in the upper medulla the nucleus lies along the ventro-medial surface of the restiform body; it enlarges in bulk and approaches the surface near the middle of the medulla where it produces the tuberculum ciner eum and it is then continued down into the cord as a cap of the posterior columna of gray substance. In the lower part of the medulla the nucleus underlies the visible part of the tractus spinalis nervi trigemini.
The sensory root of the trigeminal nerve (fifth) enters the pons on its ventral surface in line with the roots of the seventh, eighth, ninth, tenth and accessory nerves (Fig. II r). The root fibers divide T-like; the short ascending branches end in the pontine and mesencephalic nuclei of the fifth nerve and the long descending branches, forming the spinal tract, terminate in the nucleus of that tract. A certain few of these root fibers go directly to the motor nucleus of the trigeminal nerve and perhaps to other motor nuclei; these are reflex in function.