The nuclear pattern of the non‐tectal portions of the midbrain and isthmus in primates

The various nuclear groups in the midbrain of primates show marked resemblances to their homologues in subprimate forms, although certain regions are characterized by a marked increase and others by a definite decrease in development. The literature dealing with special regions is considerable in amount and some of it is of relatively early date. That pertinent to the present consideration of these regions has been reviewed under the account of the general literature placed at the end of this series of papers. Attention is called here to a few contributions that have been particularly helpful in the preparation of the primate descriptions. Among such are the studies of Ziehen on various regions of the midbrain, particularly his account of the periventricular regions, and the descriptive analysis of Ingram and Ranson ('35) of the nucleus of Darkschewitsch and the interstitial nucleus of the medial longitudinal fasciculus, which confirmed Stengel's ( '24) earlier account. There are innumerable figures and descriptions of various parts of the oculomotor and trochlear gray in primates. Among these may be mentioned the work of Panegrossi ('04), Ram6n y Cajal ('ll), Brouwer ('18, and elsewhere), Le Gros Clark ( '26) and Mingazzini ( '28). The differences in nomenclature with respect to the periventricular gray of caudal midbrain and isthmus regions are indicated