738 THE CEREBRAL CORTEX. 



the thumb. Much more commonly, however, the movements provoked 

 are complicated by others. Thus in some individuals even minimal 

 stimulation of what has been termed the hallux centre produces move- 

 ments, not only of the hallux but also of other toes, and even of the 

 foot and leg ; and stimulation of the middle of the ascending parietal 

 may cause not only flexion of the fingers but also extension of the 

 wrist. Such movements may succeed one another, or they may be 

 simultaneous. It has been usual to speak of the movement which is 

 most often or most readily obtained on excitation of a particular 

 localised area, as the "primary" movement, and the others as 

 " secondary." 



Undoubtedly the most striking character of many of the movements 

 which are provoked by cerebral excitation is their co-ordinated and 

 purposeful nature. In conformity with this, we find that they are 

 rarely produced by contractions of a single muscle or group of muscles, 

 but it is frequent for a succession of movements to occur, and these 

 are very closely imitative of natural voluntary movements of the 

 animal. Thus the successive movements involved in prehension are 

 very easily called into play by excitation of certain portions of the 

 arm area, and a series of complicated masticatory movements by excita- 

 tion of the lower part of the face area. 1 But if the excitation is only 

 momentary, it is sometimes possible, as already mentioned, to obtain 

 the contraction of only a single muscle, such as the opponens pollicis ; 

 nevertheless the movement produced in this case may be perhaps 

 regarded as purposeful. On the other hand, it must be admitted that 

 it is frequently difficult to recognise any purpose or any approach to 

 the natural actions of the animal in some of the movements and 

 combinations of movements which are provoked by artificial excitation 

 of the cortex ; but this is more especially the case when the cerebral 

 surface is in an abnormally excitable condition, in which case the 

 effect of the excitation appears to spread to areas which are not 

 naturally involved. 



These general remarks may serve as preface to the following details 

 of the results obtained by stimulation and localised lesion respectively, 

 within the limits of the motor sphere of the cortex, as previously 

 defined. The results obtained by stimulation are shown in Figs. 337 

 and 338. 



1. The area connected with movements of the head and eyes 

 and of the ear. This area lies in front of a line which runs from below 

 upwards, either coincident with or parallel to and just behind the lower 

 limb of the precentral sulcus, at the top of which it turns sharply forward 

 to reach the mesial surface of the hemisphere. It is bounded anteriorly 

 by a line which runs nearly vertically through the anterior end of the 

 precentral sulcus. It extends over on to the mesial aspect of the first 

 frontal gyrus (marginal convolution). The part of the frontal lobe in 

 front of this line (prefrontal region) is inexcitable, 2 and the area itself is 



1 Fiirstner (Arch. /. Psychiat., Berlin, Bd. vi. S. 719) notes that in the rabbit 

 chewing movements are especially easy to obtain over a relatively large surface, and 

 FerrieT showed, that in monkeys a protraction, followed by retraction of the arm and leg, 

 as in climbing, is very readily go)t over an extensive area. From this it would appear 

 that the voluntary movements which are most habitually performed are usually those 

 which are most- easily obtained on artificial excitation. 



2 Ferrier is of opinion that the inexcitable prefrontal region is nevertheless a. part of the 

 same centre as t'iie excitable post-frontal area, for he finds that after a lesion of the pre- 

 frontal area alone there occurs descending degeneration in the mesial bundles of the 



