74 Transactions of the Academy of Science of St. Louts 
located mainly in the nucleus supraopticus but some occur also 
in both the nucleus filiformis principalis and the nucle:is filiformis 
lateralis. They are relatively large polyhedral neurons. The 
chromidial pattern consists of a complete or partially complete 
peripheral ring of coarse chromidial granules and very fine chro- 
midial dust in the remainder of the cytoplasm. 
The central somatic efferent neurons (Fig. 1 B) exhibit a 
chromidial pattern which is comparable to that of neurons which 
are known to make synaptic connections with the motor neurons 
of the cranial nerves or those in the anterior horn in the spinal 
cord. Neurons of this type occur in the lateral hypothalamic, 
the lateral mammillary, and in the dorsal hypothalamic nuclei. 
The chromidia are relatively coarse and are diffusely distributed 
throughout the cell body, including the expanded proximal por- 
tions of the dendrites. Most of these neurons are polyhedral in 
form but some are roughly spherical. In general they are very 
similar to somatic motor neurons. 
The central visceral efferent category includes the neurons 
(Fig. 2 A) whose axons terminate in relation to neurons of the 
general visceral efferent column of the brain stem or the inter- 
mediolateral cell column of the spinal cord. The central visceral 
efferent neurons vary in size but their general cytological struc- 
ture is remarkably constant thoughout the hypothalamus. The 
smaller ones tend to be spherical and the larger ones polyhedral. 
The chromidia are irregular in shape and, in general, form a 
diffuse peripheral ring, but they may tend to be aggregated in 
certain areas of the cytoplasm. Most of the hypothalamic nuclei 
of the cat contain neurons of this type. 
The associational category includes those very small neurons 
(Fig. 2 B) of the hypothalamus which are comparable both in 
size and cytological structure to the associational neurons in the 
body is spherical but may be slightly fusiform. The relative 
amount of chromidial substance varies in different nuclei but the 
