The latter fibers rise in the superior and petrosal glosso pharyngeal ganglia situated in the jugular foramen. The genetic nucleus of the efferent fibers is located inside the medulla.
Behind the ninth nerve in the same groove are the roots of the tenth and eleventh nerves. The roots of the ninth and tenth are situated between the olive and the restiform body; but, if the nerve trunks have been cut, it is impossible to de termine which of the ten or a dozen root bundles belong to each of them.
ro. The Vagus Nerve (N. vagus).—The efferent fibers of the vagus, like the glossopharyngeal, emerge from the posterior lateral sulcus, and in the same sulcus the afferent fibers enter the medulla (Figs. 2 1 and 57). It is a very complex nerve. Its efferent fibers comprise motor, inhibito-motor, vasodilator, secretory, trophic and inhibito-secretory fibers (Pawlow). The afferent or sensory fibers of the vagus rise in the jugular and nodular ganglia of the nerve (g. jugulare and g. nodosum) within and just below the jugular foramen. Within the medulla are the genetic nuclei of the efferent fibers.
The accessory nerve (n. accessorius) is composed of a cerebral and a spinal root both of which are efferent in function (Fig. 57). The cerebral root (radix cerebralis) rises within the
medulla and issues from the posterior lateral sulcus below the level of the olive and immediately inferior to the roots of the vagus. This is distributed entirely by way of the vagus. The spinal root • (radix spinalis) rises in the gray substance of the spinal cord and, having emerged from the lateral surface of the spinal cord and passed through the foramen magnum, it joins the cerebral (accessory) root near the jugular foramen.
12. Hypoglossal Nerve (N. hypoglossus).—The twelfth is the great motor nerve to the tongue (Figs. 21 and 57). A half dozen or more radicals make it up; they rise in the medulla and issue in linear series from the anterior lateral sulcus of the medulla between the pyramid and the olive. The root bundles which emerge from the same sulcus below the level of the olive belong to the anterior root of the first cervical nerve.
The student should now turn back to Table I. Study it carefully and identify all the primary and secondary divisions of the brain (Figs. 14, 15, 16, 17, i8, and 34).