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1910-11.] Topography of Cerebral Cortex of Guinea-pig. 
With the exception of the “ sensori-motor ” area jnst described, almost 
the whole of the guinea-pig cerebrum shows a sensory type of cortex. The 
cortex at the anterior pole, or Type V., is probably scarcely sensory, and 
might be classified as undifferentiated. 
No definite conclusion was come to as regards the position of sensory 
centres from an examination of the cortex, but a consideration of the work 
done on the guinea-pig by Allen and Watson led to the suggestion that a 
large part of this sensory zone must correspond to the kinaesthetic sense. 
From Miss Allen’s work particularly it is clearly shown that the kinaesthetic 
sense is the most important factor in the associative or psychical processes 
in the guinea-pig. 
In the mole, shrew, and hedgehog, Watson mapped out on the mesial 
surface a probable visual and fifth nerve centre. Careful examination of 
the mesial surface in the guinea-pig failed to discover any parallel 
formation. Round the posterior pole the cerebrum shows a “ sensori motor ” 
type of cortex, but with fewer large sub-granular pyramidal cells than in 
Type II. Since this is homologous to the visual centre as demonstrated 
in rabbits and other animals, the modified sensory type of cortex found 
here seems to suggest the probability of this being a visual centre. The 
somewhat atypical sensory cortex does not seem to contradict such a 
suggestion, since sight is not the most important sense in the guinea-pig. 
Briefly summarised, the results are — 
1. Histologically, the whole cerebral cortex may be divided into five 
distinct types of cell lamination. 
2. Electrical stimulation demonstrated the presence of a motor area 
in the posterior half of the cerebrum. 
3. This motor area was characterised by large sub-granular pyramidal 
cells. 
4. No true motor area was shown to exist, the so-called motor area 
being evidently sensori-motor. 
5. The sensory area is extremely diffuse, and, from a consideration of 
the work of Allen and Watson, the suggestion is made that a great part 
of the area is associated with the kinsesthetic sense. 
6. The suggestion is made — based on the homology of the area — that 
the visual centre is located at the posterior pole. 
I wish to acknowledge my deep indebtedness to Professor Noel Paton 
for much help and direction in the work, also to Dr T. Graham Brown 
in association with whom this investigation was begun. 
