FEATURES OF TRIGEMINAL MESENCEPHALIC NUCLEUS STRUCTURE AND ORGANIZATION .1. LIGHT MICROSCOPY

The morphology and distribution of cells in the trigeminal mesencephalic nucleus were compared in newborn and adult mice, and in adult rats and cats. No gross morphological differences indicated a somatotypic subdivision of the nucleus. Changes in cell morphology in the adult mouse as compared with the newborn, are possibly related to the relatively late innervation of muscle spindles. Cell counts indicated that cell number increased not only with growth of the animal but also with increasing complexity of the jaw musculature. Analysis of the trigeminal motor root in the adult mouse showed a unimodal distribution of myelinated fibers that numericaly could not encompass both motor and mesencephalic fibers. No provision for the Y motor system appeared to be present. A substantial proportion (1:7) of cells were in soma‐soma contact. The possible functional implications of these cell clusters were discussed. Copyright © 1969 Wiley‐Liss, Inc.