MOVEMENTS OF THE UPPER LIMB. 743 



those muscles of the opposite side which act unilaterally on stimulation, 

 but not of the bilaterally acting muscles. The opposite cheek-pouch is 

 paralysed and fills with food, but is occasionally emptied by pressure 

 by the hand. Eventually the paralysis is recovered from, and it is 

 emptied by its own muscular wall. If a second lesion is now established 

 upon the intact side of the brain, this first cheek-pouch does not show 

 renewed paralysis. 1 With a bilateral lesion there is marked difficulty 

 in swallowing and mastication, but the voice is not lost. The actions 

 of the muscles are ultimately recovered. This may be due to parts of 

 the grey matter in the depth of the fissures within the area having been 

 left, or it may be that the recovered movements are reflex, and not 

 truly volitional. 



3. The area connected with movements of the upper limb. 

 This is an extensive area (Fig. 336) occupying the upper half of the 

 central gyri (except their uppermost ends), and extending forwards 

 in the first frontal gyms, to the edge of the hemisphere, where 

 it reaches the marginal part of that gyrus (Fig. 338). It is bounded 

 in front by the area for the head and eyes, below by the facial 

 area, behind by the intraparietal sulcus, and above by an imaginary 

 line separating it from the leg area at about the level of a small 

 horizontal sulcus, which is very constant in the monkey's brain. 

 Various complex movements of the arm and hand were described 

 by Ferrier by stimulation within this area (Fig. 335). From 

 the upper part, extending over both central gyri, the opposite hand 

 was struck backwards, the arm being adducted, extended, and re- 

 tracted, and the hand pronated. Further forwards (base of first 

 frontal gyrus), extension forwards of the arm from the shoulder, as if 

 trying to reach or touch something in front. Along the ascending 

 parietal gyrus, clenching of the fist, beginning with the thumb and 

 index finger, associated with action of the wrist. On the ascending 

 frontal gyrus, in front of this, flexion and supination of the forearm. 



The retraction of the limb described by Ferrier is most readily got 

 from the ascending parietal near the upper limit of the arm area. 

 From the corresponding part of the ascending frontal it is more usual 

 to obtain, as a primary movement, a forward movement of the whole 

 arm with raising of the shoulder, and this and other movements of the 

 shoulder, combined secondarily with movements of the more peripheral 

 parts of the arm, and especially with extension of the elbow, is found 

 over the whole of the upper and anterior part of the area, merging in 

 front into combined movements of the head and shoulder. This upper 

 and anterior part of the arm area is therefore primarily concerned with 

 shoulder movements, although, secondarily, other parts of the upper 

 limb may be set in action by its stimulation. Below the shoulder 

 region is a part of the area, occupying the expanded part of the ascend- 

 ing frontal gyrus just above the level of the angle of the precentral 

 sulcus, which, as Ferrier showed (Fig. 335, 6), gives on stimulation a 

 marked flexion of the arm at the elbow, combined with supination 

 (biceps action). This is often combined as a secondary action with 

 extension at the wrist and flexion of the fingers and thumb. 



The primary effects obtained from stimulation of the ascending 

 parietal in the lower two-thirds of its extent within the arm area are, 

 as Ferrier stated, movements of the fingers and thumb. These, how- 



1 E. Flood, loc. tit. 



