270 Microscopic Structure of Cortical Areas 
not come from the periphery, but may come from different regions of the 
cortex. 
Aupitory REGION. 
This center is, judging from its structure, still a part of the seven- 
layer type, but as the localization is known with a fair degree of cer- 
tainty, I will describe it, as others have done, as the auditory center. 
Experimental investigation made on animals has shown that the tem- 
poral lobe is the seat of the auditory center. Thus, Munk has caused 
deafness by extirpating the temporal lobe in monkeys; and in man, on 
the basis of clinico-pathological observations, the auditory center was 
also located in the temporal lobe. Flechsig has followed the auditory 
fibers from the lower auditory centers directly to the transverse tem- 
poral gyri and to the superior temporal gyrus opposite the transverse 
gyri. 
I have succeeded in preparing sections of the temporal lobe of the 
pteropus, cat, dog and monkey; but in the brain of the horse the stain 
of the sections was not a good one, and of the human brain the greater 
part of the temporal lobe was injured in preparing. [ shall, therefore, 
be able to describe this, as well as several other portions of the cortex in 
man and the horse, only later on. 
In the pteropus I have not been able to find any important dif- 
ferences from the general type; in the cat and dog indistinctly; but in 
the monkey I have found more plainly the following deviations from the 
contiguous parietal type. In the temporal lobe, principally two layers 
of cells increase in size—the granule layer and inner layer of poly- 
morphous cells. One can also notice that in the inner layer of pykno- 
morphous pyramidal cells the pyramidal cells increase in number, this 
being not so conspicuous as the increase in the two aforementioned lay- 
ers. The inner layer of pyknomorphous pyramidal cells adjoins a little 
more closely the granule-cell layer, and therefore the stripe of Baillarger 
is plainly visible between the inner layer of polymorphous cells and the 
inner layer of pyknomorphous pyramidal cells, thus suggesting a struc- 
ture of eight layers. The most striking feature of the cortex in the 
auditory region is the enormous increase of cells in the granule cell layer, 
and in the inner layer of polymorphous cells, as compared with what is 
found elsewhere in the seven-layered cortex. 
VISUAL CENTER. 
The visual center has aroused the greatest interest on account of ex- 
perimental and clinical observation. But up to the present, it still 
seems unsettled as to where it is located and how far it extends in the 
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