THE CEREBRUM 595 



The Motor Area of the Chimpanzee Brain. In a series of experi- 

 ments made by Sherrington and Grunbaum on the brain of the chimpanzee 

 it was discovered that the so-called motor area was not so widely distributed 

 as in the monkeys generally, but was confined almost exclusively to the 

 convolution just in front of the fissure of Rolando, as it was impossible to 

 obtain any movement on direct stimulation of the convolution just behind it. 

 All points on the surface of the pre-central convolution, including the portion 

 forming the wall of the Rolandic fissure itself, were found to be excitable 

 and productive of movement when stimulated. The sequence of representa- 

 tion from below upward is similar to that observed in the monkey. One 

 peculiarity, however, was the location of the area for conjugate deviation of 

 the eyeballs to the opposite side. This is situated far forward in the middle 

 and inferior frontal convolutions, and separated from the areas in the pre- 

 central convolution by a region apparently inexcitable. These facts are of 

 great interest and value in the assignment of the motor areas in the cortex 

 of the human brain, as in its development and configuration the chimpanzee 

 brain more closely resembles the human brain than does the monkey's. 

 The Localization of Sensor and Motor Areas in the Human Brain. 

 The observation of clinical symptoms and their interpretation by post-mortem 

 findings, the phenomena observed during surgical procedures, and the results 

 of embryologic investigations, point to the conclusion that corresponding 

 areas both for sensations and movements exist in the cerebral cortex of the 

 human brain, though it is probable that their locations do not in all respects 

 coincide with those characteristic of the monkey or even the ape brain. In 

 the following diagrams (Figs. 247 and 248), the sensor and motor areas are 

 at least provisionally located, in accordance with recent observations. They 

 are represented as limited or bounded by a serrated line to indicate, as 

 suggested by Mills, that they are not sharply delimited, but that they inter- 

 fuse or interdigitate with surrounding regions. 



In the following paragraphs these areas are considered in the order of 

 their development and physiologic activities. 



The Sensor Areas. The sensor areas occupy regions corresponding in 

 a general way with those of the monkey brain. 



i. The Cutaneous Area. The area of cutaneous or tactile sensibility has been 

 assigned to the post-central convolution on the lateral aspect, and to a 

 portion of the super-frontal convolution and the lower half of the para- 

 central lobule on the mesial aspect of the hemicerebrum. It has been 

 stated by Flechsig, who bases his statements on the results of embryo- 

 logic investigations as to the course, time of myelinization and termina- 

 tion of certain afferent tracts, that the cutaneous area must also be 

 assigned though perhaps in less degree to the pre-central convolution 

 as well. 



Clinic observations and post-mortem findings, together with the results 

 of more recent experimental investigations make it extremely probable that 

 the cutaneous area is confined entirely to the regions posterior to the central 

 fissure or fissure of Rolando. Dr. Charles K. Mills, whose skill in interpret- 

 ing the phenomena of the diseases of the brain is well known, states in this 

 connection, that "innumerable cases have been reported of lesions of the 

 motor (the pre-central convolution) without the slightest impairment of sen- 

 sibility." In many instances portions of the motor cortex of the human 



