352 ELIZABETH CAROLINE CROSBY 
cortex takes its characteristic position and dorsal to it appears 
a group of scattered cells of a larger size which, judging from their 
fiber connections, are strongly under the influence of the dorso- 
medial portion. This latter group constitutes Adolf Meyer’s 
dorsal portion of the hippocampus and is the ‘subiculum’ de- 
scribed by Johnston (715) in turtles. Except at the very an- 
terior end of the hemisphere, the hippocampal formation and 
the cortex of the pyriform lobe are separated by the general 
pallium. Ventralward, the dorso-medial portion of the hippo- 
campus is continuous with a diffuse mass of small cells, the 
primordium hippocampi. 
In the more anterior part of this dorso-medial region of the 
hippocampus, the cells, as seen in Golgi preparations, are goblet- 
shaped and are comparable with the cells of the secondary ol- 
factory nuclei. They are more nearly related in type to the small 
projection cells of the hippocampus. The most anter:or portion 
of the hippocampus probably does function to considerable de- 
gree at least, as a secondary olfactory nucleus. Other cell types 
found in the hippocampus are as follows: 
1. Correlation cells (fig. 31). The correlation cells of this 
type are found in the dorsal portion of the dorso-medial area at 
the anterior part only, so far as is known. They are especially 
interesting because of their resemblance to the cells of the hippo- 
campal regions in Amphibia (Herrick, 710). These are prob- 
ably phylogenetically the oldest of the highly specialized cells 
of the hippocampus. 
2. Double pyramid cells (figs. 35, 36). These are the cells 
which especially give character to the dorso-medial portion of 
the hippocampal cortex. Their cell bodies are large and more 
or less pyramidal in form. Thick, thorny, bushy dendrites 
spread out lateralward and medialward from the cell body but 
are especially thick on the medial side, where they can often 
be seen breaking up around the terminal arborizations of the in- 
coming medial olfactory, parolfacto-cortical and tuberculo- 
cortical tracts. Sometimes the impulse reaches the double pyr- 
amid cell through an interpolated neurone. The dendrites which 
are directed lateralward, receive olfactory impulses from the 
