THE FOREBRAIN OF THE ALLIGATOR 351 
Cortical centers of the hemisphere. Within the pallium three 
types of cortical centers may be distinguished. One of these, 
the hippocampus, is concerned primarily with olfacto-visceral 
correlations. The pyriform lobe cortex is concerned chiefly 
with olfacto-somatic correlations, with some involvement of the 
general visceral centers of the hypothalamus. The third type, 
the general cortex, is largely concerned with somatic correla- 
tions, and is differentiating toward true neopallium. 
Hippocampus (figs. 3 to 10, 12, 14 to 21). Spitzka was the 
first to suggest that the dorso-medial wall of the hemisphere was 
hippocampus, although he still called the hippocampal com- 
missure the corpus callosum. From that time the homology of 
this medial cortex has been recognized by most observers, includ- 
ing Edinger, Brill, Meyer and Elliot Smith. Very good sum- 
maries of the earlier studies on the hippocampus and its com- 
missure are given in Elliot Smith’s article (03) dealing with 
the morphology of the cerebral commissures in vertebrates and 
in the Arris and Gale lectures (10). In this connection it is 
interesting to note that Johnston (15) has reopened the ques- 
tion of the presence of true callosal fibers in the dorsal or hip- 
pocampal commissure of both marsupials and reptiles. His evi- 
dence for their presence is based on expérimental work. In 
regard to reptiles he says, page 404, ‘‘in the turtles the lack of 
medullation in the dorsal commissure has made it impossible 
thus far to secure positive evidence as to the presence of callosal 
fibers.’”’ He argues that they should be present because of the 
great number of ascending fibers carrying sensory impulses from 
the thalamus to the telencephalon in reptiles. Others, as Ra- 
mon y Cajal, Unger, and Pedro Ramon, have claimed that various 
reptiles have true callosal fibers. 
Adolf Meyer (92) was the first person to distinguish between 
the dorsal and the dorso-medial portions of the hippocampus. 
The dorso-medial portion arises rostrad in the narrow part of the 
olfactory crus and there occupies a somewhat dorsal as well as 
a dorso-medial position (fig. 3). At this level it lies in close 
relation dorso-lateralward with the cortex of the pyriform lobe. 
As it extends caudad into the hemisphere, the dorso-medial 
