Small nucleus in the brainstem of human, located adjacent and medial to the nucleus prepositus in the dorsal medulla, described in several atlases of human brain stem. In transverse sections, it is oval with its long axis aligned with the dorsal border of the brainstem. It begins at about the same A-P level as the nucleus prepositus, just rostral to the hypoglossal nucleus. It includes calretinin immunoreactive large cells with oval or polygonal cell bodies. Cells are not immunoreactive for either calbindin or parvalbumin, but a few fibers immunoreactive to each protein are found within its central region. Cells in PMD are also immunoreactive to nNOS, and immunoreactivity to a neurofilament protein shows many labeled cells and fibers. According to Baizer et al., no equivalent structure was observed in the cat, rat, mouse or monkey atlas although they did not look at the brains of the great apes. [ ]