360 ELIZABETH CAROLINE CROSBY 
visceral centers, a lateral group which is the place of termina- 
tion for the somatic impulses brought in by the optic and lem- 
niscus systems and, intermediate between these two groups, a 
third nucleus which receives fibers of both the visceral and 
somatic type. This nucleus is the nucleus medialis or the 
nucleus rotundus of some authors. 
In the medial group are the nucleus anterior and the nucleus 
magnocellularis. The nucleus anterior (figs. 10 and 11, 20), as 
its name implies, lies at the very anterior end of the thalamus. 
It is dorsal in position and its cells are smaller and more closely 
packed together than are the cells of the lateral nucleus. It re- 
ceives fibers from the hypothalamus and is connected with the 
small celled ventro-medial part of the hemisphere by means of 
a fiber tract. 
The lateral group includes the nucleus lateralis, a special 
derivative of this nucleus—the pulvinar—and another optic 
center which most writers have termed the corpus geniculatum 
laterale. The nucleus lateralis is conspicuous because of the 
large size of its neurones. The cell bodies of these neurones 
(figs. 41, 42, 43) are large, goblet or triangular in shape, and have 
thick thorny dendrites which extend out in every direction from 
the cell bodies. The axones enter the lateral forebrain bundle. 
This nucleus is lateral in position, being lateral and somewhat 
ventro-lateral to the nucleus anterior and lateral to the nucleus 
medialis (or rotundus). It receives lemniscus fibers and some 
optic fibers and, with the lateral thalamic optic centers, repre- 
sents the beginning of the neothalamus (Edinger) of higher 
forms, i.e., that lateral portion of the thalamus which serves 
as a place of synapse for nervous impulses passing to the neo- 
pallium and which develops parallel with the development of 
the neopallial cortex. In the more posterior part of the thala- 
mus, a lateral portion has begun to differentiate away from this 
nucleus and to form a beginning of the pulvinar. This separate 
nucleus is developed under the direct influence of the incoming 
optic fibers. 
There are other cell masses in the thalamus proper, as for 
example the nucleus reuniens figured in the alligator brain by 
