Brainstem

The cross-section of the spinal cord is oval whereas that of the rhombencephalon looks more like an opened book. The roof of the 4th ventricle is stretched out. The columns of nuclei are aligned along a medio-lateral axis instead of a ventro-dorsal axis. The columns of the basal plate are supplemented by special visceral efferents (SVE) which innervate the muscles of the pharyngeal arches. Two additional nuclear columns appear in the alar plate: special visceral-afferents (SVA, for the sense of taste) and special somatic afferents (SSA, for hearing and sense of balance). There are seven columns of nuclei in total. If the roof were removed, it would be possible to look onto the floor of the 4th ventricle, which is bordered in the area of the alar lamina by the rhombic lip.