70 THE NERVOUS SYSTEM 



is still incomplete, and there is doubt as to its substantial value. It 

 is, however, customary and so provisionally proper, to describe certain 

 areas of the cortex as motor and sensory, the latter especially having a 

 definite and more or less certain value. Other regions are called asso- 

 ciation-areas. 



THE MOTOR AREAS OF THE HUMAN CEREBRUM, in which it has 

 been supposed that voluntary or deliberate muscular movements are 

 actuated; are thought at present to be the convolutions anterior to the 

 fissure of Rolando, the adjoining posterior part of the frontal lobe, and 

 that portion of this general region to be seen on the mesial surface of the 

 hemispheres. In the earlier work of Ferrier, Horsley, Munk, and others 

 on monkeys the motor area was found to occupy the posterior central 

 convolution also, but it has lately been made probable by Sherrington and 

 Griinbaum, working on the chimpanzee (the brute most like man), and 

 by the embryological studies of Flechsig, that the area just posterior to 

 the Rolandic fissure represents in man cutaneous sensation. Farther 

 back the important muscular and joint sensations, known as the kines- 

 thetic impulses, are represented. These facts, however, are simply the 

 products of stimulation of the cortex and of the other modes of experi- 

 mental study largely on speechless animals. It is likely, on the whole, 

 that the kinesthetic sensations of a muscular part have their " centers" in 

 the same brain-areas as do the movements of these parts. We are not 

 then certain at the present time what we mean by "a motor area/' since 

 all sorts of sensations, feelings, ideas, etc., are closely related to the con- 

 traction of muscles. Adamkiewicz has recently claimed, as a result of 

 four years of careful research, that the whole cerebral cortex is, properly 

 speaking, psychical, or at least psychomotor, in its functions. He sup- 

 poses, accordingly, that it is the function of the cerebellum to conduct 

 unconscious movements. Still, stimulation of the Rolandic area above 

 defined causes contraction of the cross-striated muscles in different parts 

 of the body. 



The motor area of each side of the brain represents the muscles of the 

 other side of the body, for a large proportion (90 per cent.) of the efferent 

 paths that run thence cross to the opposite side in the lower part of the 

 medulla. Another sort of reversal is present in the Rolandic motor area. 

 The higher in the erect human body a muscular group is, the lower in 

 general is its center along the lateral surface of the anterior central con- 

 volution. The muscles of the face are thus represented in front of the 

 lower end of the fissure of Rolando and those of the toes at its upper 

 end. Above the centers for the head muscles are those of the neck, then 

 upward those of the wrist, arm, shoulder, trunk, and hip. The centers of 

 the leg extend in reverse order thence to the median longitudinal fissure, 

 on or near which are situated the motor nuclei of the toes. 



When this region of the cortex is stimulated with any suitable agent, 

 as, for example, a weak alternating induced electric current, contraction 

 takes place in the corresponding muscle or muscle-group on the other 

 side of the body. If the stimulus be too strong or continued too long, 



