72 Transactions of the Academy of Science of St. Louts 
neurons of the substantia grisea centralis vary in size in different 
areas and are more densely packed in some regions than in others, 
they probably all represent one functional type and should be 
considered as incorporated in a single nucleus. On the basis of 
a study of the hypothalamus of the albino rat, Krieg (1932) 
concluded that the nuclei filiformis, supraopticus, lateralis, pre- 
mammillaris lateralis, and mammillaris lateralis appear to consist 
of cells of the autonomic type. 
Ingram et al (1932) described nineteen groups of cells in 
the hypothalamus of the cat. Crouch (1934) reported twenty- 
one nuclei in the hypothalamus of Macacus rhesus. He found 
that the nuclei are not as clearly set off from neighboring groups 
in Macacus rhesus as they are in lower mammals but most of the 
nuclei are homologous to the corresponding hypothalamic nuclei 
of lower mammals. 
The present work has been undertaken to examine the nuclei 
of the hypothalamus of the cat which have been identified on the 
basis of their separation from neighboring nuclei and point out 
the correlation between the cytological structure of their constt- 
tuent neurons and the functions which they must subserve be- 
cause of their anatomical connections. 
MATERIALS and METHODS 
The present investigation is based on serial sections of the 
brain stems of cats, cut to a thickness of eight microns. The 
material was fixed in a forty percent aqueous solution of mercuric 
chloride. Fixation was facilitated by transfusion with the fix- 
ative through the common carotid artery of the freshly killed 
animal. After two hours the brain was removed and the portion 
of the brain stem in question placed in the fixative for two days. 
