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1906-7.] Functions of the Rolandic Cortex in Monkeys. 
No indication appears to be afforded by the study of myelination of the 
boundary between areas of the cortex, which is shown by the method of 
electrical excitation to lie within the fissure of Rolando. 
Considerable advances have been made in recent years in the study of 
the histological structure of the cortex cerebri, and areas have been mapped 
out upon it by Brodmann, Campbell, and others characterised by differences 
in the arrangement of fibres and in the size, shape, and position of the 
cells. 
An area in the ascending frontal convolution and adjacent portion of the 
marginal convolution is found to differ with regard both to fibre and cell 
arrangement from the cortex anterior and posterior to it. Its characteristic 
feature is the presence of very large cells — giant cells — described by Betz 
and Bevan Lewis. The anterior and posterior boundaries of the area con- 
taining these giant cells, as mapped out by Brodmann * in the brain of 
Cercopithecus, correspond closely with the limits of the region from the 
excitation of which we have obtained movements of the lower and upper 
extremities, body, neck, and upper part of face. It is interesting to observe 
that the posterior boundary of this area in its lower part leaves the fissure 
of Rolando and passes downwards in a manner similar to the posterior 
limit of excitability as determined by us. This region is termed by 
Brodmann the area giganto-pyramidalis, and corresponds with the pre- 
central area of Campbell. Anteriorly it lies contiguous to the area 
agranularis of the former author, while behind it joins the area paradoxa or 
post-central area of Campbell. 
The lower part of the face area, viz., that from which movements chiefly 
of mastication and deglutition are obtained, is considered by Brodmann to 
form an area of cortex differing in histological structure from the area 
giganto-pyramidalis but identical with the region in the frontal lobe, from 
stimulation of which we have described movements of the head as resulting. 
The region in the angle of the precentral sulcus, from which lateral move- 
ments of the head and eyes are obtained, is characterised also, according to 
the same author, by a separate and distinct histological structure. 
We have examined the microscopic structure of the excitable area in the 
species of monkeys employed by us with the object especially of determining 
the posterior limit. This we find, taking the presence of giant cells as the 
most reliable guide, to lie in the lower part of the anterior lip of the 
Rolandic fissure in the greater part of its length. 
Within the motor area further histological differentiation is possible. It 
was shown by Bevan Lewis *j- that the giant cells, termed by him “ motor 
* See fig. 62 in Vogt’s paper, loc. cit. t Brain , 1878, vol. i. p. 79. 
