The morphology and connections of the posterior hypothalamus in the cynomolgus monkey (Macaca fascicularis). I. Cytoarchitectonic organization.

The cytoarchitectonic organization of the posterior hypothalamus of the cynomolgus monkey (Macaca fascicularis) was analyzed in Nissl, Golgi, acetylcholinesterase, and reduced silver preparations. The region consists of a number of cell masses that differ considerably in their discreteness and in the homogeneity of their neuronal populations. The nuclei identified include: the medial mamillary nucleus (in which at least three distinct subdivisions can be recognized--a pars medialis, a pars lateralis, and a pars basalis); the small-celled nucleus intercalatus; the large-celled lateral mamillary nucleus; a single premamillary nucleus; the tuberomamillary nucleus; the posterior hypothalamic nucleus; the caudal extension of the lateral hypothalamic area; the supramamillary area; and the paramamillary nucleus (which appears to correspond to the nucleus of the ansa lenticularis of other workers). As a basis for the subsequent experimental study of the efferent connections of the posterior hypothalamus, the location of each of these cell masses is described and illustrated in a series of low-power photomicrographs, as are the form and distribution of the resident neuronal populations of the various components of the mamillary complex as seen in Golgi preparations.