THE FOREBRAIN OF THE ALLIGATOR 365 
it is probable that the majority of fibers between the lateral 
parolfactory nucleus and the hippocampus conduct in the de- 
scending direction and that the nucleus functions as a place 
of synapse between the hippocampal cortex and the lower brain 
centers. 
So far as the present data go they appear to suggest a division 
of labor between the medial and the lateral parolfactory regions 
(medial and lateral septal nuclei of some authors) and to suggest 
a motive for their differentiation, viz., that the medial nucleus 
is a way-station for ascending impulses going toward the hippo- 
campus and the lateral nucleus is a similar station for descend- 
ing impulses coming from the hippocampus. The writer is 
aware that the data are insufficient for a definite conclusion and 
that experimental researches or even more favorable Golgi ma- 
terial may prove these suggestions erroneous. 
Commissures of the forebrain 
There are two large commissures in the forebrain, the hippo- 
campal commissure and the anterior commissure. 
Commissura hippocampr (figs. 18, 19). The fibers of this com- 
missure arise as axones of the projection cells of the hippocam- 
pus, which run ventralward and across the mid-line just above 
the anterior commissure. After crossing, some of the fibers 
appear to end in the nucleus commissuralis, but most of them 
pass dorsalward and end in synaptic relation with the cells of 
the opposite hippocampus. Thus the hippocampi of the two 
sides are put into connection with each other and enabled to work 
in a correlated way. 
The commissura hippocampi has been the cause of much dis- 
pute among the earlier neurologists. Osborn (’87) identified 
it as the corpus callosum and for a time this interpretation was 
generally accepted. Adolf Meyer (’85) showed it to be the com- 
missure of the medial and dorso-medial wall, which regions he 
identified as hippocampus. Elliot Smith (’03) claimed that in 
reptiles and monotremes there were no eallosal fibers in the 
dorsal commissure. Johnston (13a, pp. 402-404) is quite 
