Cross Section at the Level of the Vagus Nerve
The fourth ventricle has become wider. The same nuclear columns as in A are found in its floor. Ventrally to the hypoglossal nucleus (AB3) appears Roller’s nucleus (B24) and dorsally the intercalate nucleus (Staderini’snucleus) (B25); the fiber connections ofthese two nuclei are not known. In the lateral field, the nuclei of the posterior funiculus disappear and make room for the vestibular nuclei (medial vestibular nucleus)(B26). In the middle of the medulla oblon-gata, the decussating fibers form a seam, the raphe (B27). On both sides of the raphe liesmall groups of cells, the raphe nuclei (B28); their serotoninergic neurons project to the hypothalamus, the olfactory epithelium, and the limbic system. Along the lateral aspect, spinal fibers running to the cerebel-lum aggregate in the inferior cerebellarpeduncle (restiform body) (B29). Afferentand efferent fibers of the vagus nerve (B30) cross the medulla oblongata. Ventrally to them, the spinothalamic tract (B31) and the spinocerebellar tract (B32) ascend along the lateral aspect. The olivocerebellar fibers (B33), which run to the inferior cerebellar peduncle, aggregate dorsally to the olive.