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80 Transactions of the Academy of Science of St. Louis 
A). It is a poorly defined aggregate of small to medium-sized 
neurons. The medium-sized ones are central visceral efferent 
neurons and form the greater part of the nucleus. Among them 
are located small associational neurons. 
Nucleus Hypothalamicus Ventrolateralis:, The nucleus hy- 
pothalamicus ventrolateralis lies medial and ventromedial to the 
anterior pillar of the fornix (Fig. 3 B). It is separated from 
the ventral margin of the hypothalamus by undifferentiated gray 
matter. The central somatic efferent neurons outnumber the 
associational neurons, which are uniformily distributed among 
them. Reports of known fiber connections are wanting. The 
cytological structure of the neurons suggests connections with 
neighboring hypothalamic nuclei through the associational neurons 
and with preganglionic neurons at lower levels in the brain stem 
through the central visceral efferent neurons. 
Nucleus Mammillaris Medialis: This nucleus consists of 4 
large dorsomedial and a smaller ventrolateral portion (Fig. 3 
D). The former includes mainly central visceral efferent 
neurons; the latter associational neurons. This nucleus and the 
nucleus mammillaris lateralis form the mammillary body. All 
the neurons in the nucleus mammillaris medialis are poorly sup- 
plied with chromidia, especially those in the ventrolateral portion. 
The chromidia are finely granular and tend to have either an 
extreme peripheral or perinuclear distribution. In the latter case 
they form a rather complete, thin, dark ring. The fibers of the 
mammillo-thalamic and mammillo-tegmental tracts arise mainly 
in this nucleus. Gurdjian (1927) found that the commissural 
portion between the mammillary bodies contains cells whose 
processes connect the nuclei of the opposite sides. 
Nucleus Supramammillaris: This nucleus is quite com 
pletely isolated, although the neurons are not compactly arranged. 
It is located along the dorsomedial margin of the cerebral pe- 
duncle in the extreme lateral portion of the hypothalamus. 
Central visceral efferent and associational neurons are uniformily 
