M. G. Schlapp 261 
an animal will probably occupy more space than those not so highly 
developed, and thus displace the other less developed centers, so that 
these may come to occupy a position different from that in other ani- 
mals. Thus according to the experimental investigations of Munk, the 
visual center in the monkey of lower types is in the operculum; but an 
attempt to locate it in man in the corresponding region would result 
in great confusion, as it is not situated on the lateral surface of 
the hemisphere in man as in the monkey, but on the medial surface. 
This displacement of the visual center in man is very likely brought 
about by the more highly developed association centers which occupy 
the lateral surface of the hemisphere in the parietal and occipital lobes. 
It is true, some investigators still adhere to the idea that the visual 
center is situated on the lateral surface of the hemispheres, but such 
is not the case in man. 
Asa result of one or more of the sources of error just enumerated we 
find the following greatly differing views maintained : 
Meynert found five layers almost everywhere in the cortex, except in the 
occipital lobe where he described eight layers. Other investigators, as for 
instance Ramon y Cajal, consider only four layers as the common type, 
the cortex presenting, however, here and there a few slight variations 
which can yet be considered part of the four-layer type. In his later writ- 
ings, Ramon y Cajal differs slightly from his former opinion. He says, con- 
cerning the sight-center in the occipital lobe, “‘ The investigations which I 
have made on the human cortex, as well as on that of the dog and cat by 
both Nissl and Golgi methods, have led me to distinguish the following 
layers: 
1. Plexiform layer (called molecular layer by authors generally, and 
* cell-poor layer ” by Meynert). 
2. Layer of small pyramids. 
3. Layer of medium-sized pyramids. 
4. Layer of large stellate cells. 
5. Layer of small stellate cells. (Called “ layer of granules” by other 
authors.) : 
6. Second plexiform layer, or layer of small pyramidal cells, with arched 
axon. 
7. Layer of giant pyramidal cells (solitary cells of Meynert). 
8. Layer of medium-sized pyramidal cells, with arched ascending axon. 
9. Layer of fusiform and triangular cells (fusiform-cell layer of Meynert). 
In the human motor cortex Ramon y Cajal recognizes the following 
layers: 
1. Plexiform layer (layer poor in cells of Meynert, molecular layer of 
some writers). 
2. Layer of small and medium sized pyramids. 
3. External layer of giant pyramids. 
4. Layer of small stellate cells. (Granule-cell layer of authors.) 
18 : 
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