THE FOREBRAIN OF THE ALLIGATOR 339 
Laterally the tuberculum olfactorium lies in close relation to 
the pyriform lobe, although its cortical layer is separated from 
the latter by an area of scattered cells which belong apparently 
with the nucleus of the lateral olfactory tract (see discussion 
of that nucleus). Medially the tuberculum olfactorium is in 
close relation with the parolfactory region. 
The relations described here are in all essential points the same 
as those described for the tuberculum olfactorium of turtles 
(Johnston, 715). The differences in the two forms are to be found 
in the somewhat higher development of the islands of Calleja 
in the turtle and in the absence in the turtle of so well developed 
a cortical layer as is found in the alligator. The tuberculum 
olfactorium does not appear as a clearly defined nucleus in 
Amphibia. In certain Dipnoi (Lepidosiren) described by Elliot 
Smith (08) it appears in an exaggerated form. The Golgi 
material available does not show the cell forms in this region. 
Nucleus commissurae hippocampi (figs. 18 and 19). This 
nucleus is really only a specialized portion of the primorium 
hippocampi, consisting of clusters of cells of that primordium 
which are mingled with the descending hippocampal fibers and 
which collect particularly about the point of decussation of the 
fibers of the hippocampal commissure. The cells of this nucleus 
serve as a place of synapse for commissural fibers and as cells 
of origin for some of the fibers of the medial cortico-habenular 
tract. In fact cells of this nucleus accompany this latter tract 
until it enters the stria medullaris and are probably a remnant 
of the broad gray connection found in lower forms between the 
hippocampal and the habenular regions. 
Nucleus commissurae anterioris (fig. 18). This name has 
been given to the cells forming the bed nucleus of the anterior 
commissure. They resemble in general character the cells of 
nucleus preopticus but are quite distinct in type from those 
forming nucleus commissurae hippocampi. The cells of the 
nucleus commissurae anterioris afford a place of synapse for 
some of the fibers of the commissural division of the stria 
terminalis. 
