M. G. Schlapp 263 
1. Pteropus. 2 Horse. 3. Cat. 4. Dog. 5. Monkey (Macacus 
Cynomolgus), and 6. Man.’ 
OLFACTORY REGION. 
The olfactory center is of variable extent in the animals examined, 
being largest in the horse and smallest in man. ‘That portion of the 
cortex which can undoubtedly be considered the olfactory cortex, pre- 
sents in the pteropus, horse, cat, dog, monkey, and man, a rather char- 
acteristic structure, which is due to the fact that the cells in the outer 
polymorphous cell layer, arrange themselves in smaller and larger 
groups, thus giving to this layer an interrupted appearance. In some 
places, especially in the olfactory tract, these cells le so close together 
(not in groups) and are so deeply stained, that one can distinguish 
plainly between this layer and the same layer in other cortical centers. 
In the pteropus, this peculiar structure extends over a comparatively 
large area of the ventral and lateral parts of the hemisphere; its limits 
are difficult to describe precisely, owing to the fact that this brain con- 
tains no fissures which could be used as landmarks. 
In the dog, cat, and monkey, this type is limited to the hippocampal 
gyrus and seems to extend into the posterior portion of the gyrus forni- 
catus; it then passes into the olfactory tract, where nearly all the pyra- 
midal cells disappear, only a few polymorphous cells remaining in 
place of the pyramidal cells. 
In the human cortex this type is confined to a very small area in the 
hippocampal gyrus bordering on one side, on the formatio cornu ammo- 
nis, of which it seems to be the continuation, while on the other side it 
is in contact with the seven-layer type. 
One can plainly see, when approaching the olfactory region from the 
seven-layer type (to be described under a separate heading), the granule- 
cell layer disappear and the pyramidal cells diminish in number and 
finally seem to be transformed into polymorphous and spindle shaped 
cells, which lie between the characteristic outer layer and inner layer 
of polymorphous cells. 
In the cortex of the horse’s brain, this type occupies a more promi- 
1 Of the horse and of man, I lost considerable material, especially the temporal lobe 
of man, so that at present my sections will not suffice to give a complete picture of 
the cortex of horse and man. I have, however, noted in the body of the text certain 
observations, and should add here that, in a horse’s brain, the finer structure differs 
from that of the cortex of other animals in that one sees clearly, with the exception 
of a few limited regions, six layers in which two stripes, the stripes Gannari or 
Baillarger, can be plainly seen. 
