4 Edward F. Malone. 



Pars Mamsiillaris Hypothal.\mi. 



Before proceeding to describe the cell groups of the pars optica hypo- 

 thalami (telencephalon) it will be necessary to consider those of the 

 pars mammillaris hypothalami (diencephalon), since the cell groups 

 of these two subdivisions of the hypothalamus are most intimately 

 related and cannot be intelligently studied separately. In 1910 

 appeared my monograph " Uber die Kerne des mensehlichen Dienceph- 

 alon " in which the cell groups of the pars mammillaris hypothalami 

 of man were described, together with a brief consideration of certain 

 closely related cell groups of the pars optica. Since the publication of 

 this monograph I have studied both portions of the hypothalamus in 

 the monkey, lemur and cat, and have compared the cell groups observed 

 in these animals with homologous groups found in man. The following 

 description of the cell groups of the pars mammillaris of the monkey, 

 lemur and cat is accordingly original and I should like to call especial 

 attention to the illustrations which clearly show for the first time the 

 different cell groups in macacus rhesus (Figs. 19 to 25). In Series 

 D of man these cell groups are also well sIiowti (Figs. 11 to 18). The 

 other series do not show much of the pars mammillaris, since it did not 

 appear advisable to add many illustrations to show exclusively portions 

 of the pars mammillaris which are not intimately related to the pars 

 optica. In the series of macacus and the Series D of man the plane of 

 section is such as to include this caudal portion of the pars mammil- 

 laris. Moreover the dorsal portion of the pars mammillaris has not 

 been illustrated, not only because it has no close relation to the pars 

 optica but also because the thalaanus of the three lower forms must 

 first be studied. Certain types of cells also which on account of their 

 location could not be confused with the cells of the pars optica have not 

 been illustrated. Accordingly it appears best to defer such numerous 

 and ekborate illustrations until the whole diencephalon can be included, 

 and to limit the illustrations of the present article to those portions of 

 the pars mammillaris which are closely related to the pars optica. 



In studying the anatomy of the cell groups of the diencephalon 

 nowhere are more satisfactory results obtained than in the hypothal- 

 aniu.s (pars mammillaris). The great difficulties encountered in 

 attempting to homologize the cell groups of the thalamus of different 

 mammals disappears when we reach the hypothalamus. This is due to 

 the fact that the thalamus is phylogenetically a much more recent 



