THE CEREBRUM 603 



The main motor areas are as follows: 



1. The Head and Eye Area. This area has been assigned to the contiguous 



portions of the medi- and sub-frontal convolutions just anterior to the 

 pre-central convolution. It is subdivided into smaller areas which initiate 

 and govern the movements of the head and eyeballs. Stimulation of 

 this area, in the chimpanzee at least, produces turning of the head to 

 the opposite side with conjugate deviation of the eyes to that side. 



2. The Face Area. This area has been assigned to the lower portion of the 



pre-central convolution and extends from below upward to about the 

 level of the genu of the central fissure. This rather large area may be 

 subdivided into (a) an upper portion including about one-third of the 

 whole and (b) a lower portion including the remaining two-thirds. In 

 both the upper and lower portions, there are groups of nerve-cells which 

 excite to action the muscles imparting movements to (a) the angle of 

 the mouth, the eyelids and jaws and (b) the movements of the vocal 

 bands or cords, the opening and closing of the mouth, the protrusion 

 and retraction of the tongue. All of these movements have their areas 

 of representation in the face area. 



3. The Arm Area. This area has been assigned to the pre-central convolu- 



tion just above and contiguous to the face area which it exceeds some- 

 what in extent. It is the largest of all the subdivisions of the general 

 area. It may be divided into at least five smaller areas, the cells of 

 which excite to action the muscles imparting movements to the thumb, 

 the fingers, the wrist, the elbow and the shoulder. 



4. The Trunk Area. This area has been assigned by Sherrington and 



Greenbaum to the pre-central convolution just superior to the arm area 

 and is rather limited in extent. Horsley located a portion of this area 

 on the mesial and lateral edges of the hemisphere in front of the leg 

 area. The nerve-cells of this area when electrically stimulated excite 

 to action the muscles which impart movements to the spinal column, 

 such as arching rotation, etc. 



5. The Leg Area. This area has been assigned to the extreme upper portion 



of the pre-central convolution and to the adjoining mesial surface, the 

 upper portion of the para-central lobule. The area on the lateral aspect 

 of the cerebrum may be subdivided into at least four smaller areas con- 

 taining groups of nerve-cells which excite to action the muscles impart- 

 ing movements to the toes, ankle, knee and hip. 



Evidence from the clinical side has demonstrated the fact that a 

 localized irritative lesion of any one of these areas gives rise to convulsive 

 movements of the muscles of the opposite side of the body, similar in 

 character to those resulting from electric simulation of the correspond- 

 ing areas of the monkey and ape brains. Destruction of these areas 

 from the growth of tumors, softening, etc., is followed by paralysis of the 

 muscles. Electric stimulation of. these areas of the human brain for 

 the purpose of localizing obscure irritative lesions prior to surgical pro- 

 cedures on the brain gives rise to similar convulsive movements. 

 The view that the cortex of the cerebrum can be divided into separate and 

 independent though physiologically related motor and sensor areas has, how- 

 ever, been questioned in recent years, and a somewhat different interpreta- 

 tion given to the facts. It is believed by many physiologists and neurologists 



