The vestibular nuclei in the macaque monkey.

The topography and the main features of the cytoarchitecture of the vestibular nuclear complex in the macaque monkey have been studied in serially cut, Nissl-stained, transverse, parasagittal and horizontal sections. In addition to the four main vestibular nuclei, the topographically closely related small cell groups (f, l, x, y, and z), distinguished by Brodal and Pompeiano ('57) in the cat, have been considered and illustrated. The vestibular nuclear complex in the macaque in general corresponds in topography and architecture to the situation described in some other mammals on which information is available, such as opossum, rabbit, cat, Galago, and man. Some dissimilarities in detail are found. For example, in man the lateral vestibular nucleus differs somewhat from the general pattern, especially in its position, and the small group f, fusing with the descending nucleus, appears to be indistinct; likewise the group y. The latter and the group z appear to be particularly well developed and easily distinguished in the macaque. The question of whether cytoarchitectonic areal differences within the vestibular nuclear complex can be correlated with differences in connections is discussed. Also in this respect there appears to be a general similarity between observations in the macaque and in other mammals. A correlation is most evident in the superior vestibular nucleus, and is rather clear in the medial and lateral vestibular nuclei and for the groups f,x,y, and z, whereas no such correlation can be found in the descending (inferior) nucleus. For several reasons it is difficult to draw reliable conclusions about comparative anatomical trends in the phylogenesis of the vestibular nuclear complex.