The perihypoglossal nuclei in the macaque monkey and the chimpanzee.

The topography of the perihypoglossal nuclei (nucleus intercalatus, nucleus prepositus, and nucleus of Roller) of the macaque and the chimpanzee was studied in serial Nissl-stained sections through the brainstem. Maps of the nuclei in the two species are presented. Although in both species the perihypoglossal nuclei are organized according to the general mammalian pattern, they show some particular features, reflecting in part, an increasing phylogenetic differentiation. In the chimpanzee the nucleus prepositus is relatively larger, the nucleus of Roller is more of a separate unit, and its cellular composition is more uniform than is the case in the macaque. A cellular connection between the two nuclei is present in the macaque (even more conspicuous in the cat, apparently absent in man), but is barely discernible in the chimpanzee. A conspicuous difference between the chimpanzee and the macaque concerns the nucleus supragenualis nervi facialis, forming a rostral continuation of the prepositus. In the chimpanzee it is a loosely structured region of small cells (as in the cat and in man). In the macaque, however, it appears as a rather well-delimited column of chiefly medium-sized cells. Some comparative anatomical and functional aspects are discussed. Many contingents of afferents to--and efferents from--the nucleus prepositus have their preferential sites of termination or origin in the nucleus, although with considerable overlapping. This indicates the presence of topical patterns in the prepositus. In general the caudal parts appear to be more related to the cooperation with the cerebellum than the rostral part, whereas the latter appears to be more particularly linked with the oculomotor apparatus.