Nuclei Tuheris Lateral es and the Ganglion Opticum Basale. 5 



portion of the brain and its development is largely dependent upon that 

 of the rapidly developing pallium. So small is the difference in the cell 

 groups of the hypothalamus of the various mammals studied that for 

 the purposes of this article one description will suffice for all. The pars 

 mammillaris hypothalami is divided into the following primary nuclei 

 (groups of cells having an identical histological character) : 



1. Ganglion mediale corporis mammillaris. 



8. Nucleus intercalatus corporis mammillaris. 



3. Nucleus tubero-mammillaris (nucleus mammillo-infundibularis). 



4. Nucleus paraventricularis hypothalami. 



5. Corpus hypothalamicum (Luysii). 



6. Substantia reticularis liypotlialami. 



7. Substantia grisea ventriculi tertii. 



At this point it is advisable to read the explanation of the various 

 kinds of illustrations as given on pp. 39-40 ; otherwise the figures, some 

 of which are immediately to be referred to, might not be correctly inter- 

 preted. 



1. Gfniglion mediale corporis mammillaris. 



This cell group constitutes the greater portion of the mammillary 

 body, and extends further caudally than the other two groups. It is 

 shown in the series of macacus (Figs. 19 and 20) and in the Series D 

 of man (Fig. 11) ; no description of its relations will be given. Con- 

 cerning its cells it will suffice to state that they are of a type readily 

 distinguishable from the other two groups of the corpus mammillare. 



2.' Nucleus intercalatus corporis mammillaris. 

 This is a small circumscribed cell group, described by me in 1910, 

 which lies between the medial and so-called lateral ganglion of the 

 mammillary body. Its location may be seen in the same figures that 

 show the medial ganglion (see above). Later Friedemann found this 

 group in cercopithecus and adopted the name here employed. The cells 

 of the nucleus intercalatus are readily distinguished from those of the 

 two other groups of the mammillar}' body through their characteristic 

 type; especially in man they have the relatively large and discrete 

 Nissl granules characteristic of efferent nerve cells. This cell group 

 should not be confused with groups which are occasionally mechanically 

 split off from the medial ganglion by fiber miasses ; the difference in 

 cell type renders this distinction easy. 



