FUNCTIONS OF THE BRAIN 929 



or rather movements, represented in the area supplied by it. A 

 tumour causes symptoms of irritation, motor or sensory convul- 

 sions beginning in, or sensations referred to, the parts represented 

 in the regions on which it presses. In connection with the localiza- 

 tion of lesions in the ' motor ' area of the cortex, and operative 

 interference for their cure, the cortex has been frequently stimulated 

 in man. There is no doubt that the ' motor ' region corresponds 

 closely in position to that of the higher apes. It does not include 

 the postcentral gyrus, for stimulation of this convolution with such 

 strengths of current as are permissible evokes no movements, while 

 movements are readily elicited from the precentral gyrus (Horsley, 

 etc.). In exposing the ' motor ' region, or any particular part of it, 

 the exact position of the fissure of Rolando becomes important ; and 

 Thane has given the following simple method for fixing it: The 

 point midway between the point of the nose and the occipital pro- 

 tuberance is fixed by measuring the distance with a tape. The 

 upper end of the fissure of Rolando lies half an inch behind this 

 middle point. The fissure makes an angle of 67 with the longi- 

 tudinal fissure (Fig. 371). The minor fissures are so inconstant as 

 to afford no safe guidance in the localization of a given area. This 

 must be delimited by stimulation. 



Sensory Functions of the Rolandic Area. There are many proofs 

 that the ' motor ' region is not a purely motor, but a sensori-motor, 

 or kincesthetic, area. Histological and embryological studies on the 

 course of the sensory paths, as already pointed out, support this 

 conclusion. It has also been mentioned that, according to Goltz's 

 observations (p. 916), removal of the Rolandic cortex causes defects 

 of sensation as well as of movement. In man, in connection with 

 operations on the brain, still better evidence has been obtained. 

 In two cases Gushing was able to elicit tactile sensations by electrical 

 stimulation of the gyrus postcentralis (ascending parietal convolu- 

 tion), and the sense of muscular movement by electrical stimulation 

 of the gyrus precentralis. In a very careful study of a case in which 

 he removed the upper Hmb area of the right hemisphere in a boy 

 for violent convulsive movements of the whole of the left arm, 

 Horsley came to the conclusion that the precentral gyrus in man 

 is the seat of representation of (i) slight tactile sensation (after the 

 operation appreciation of the lightest tactile stimuli was lost); 

 (2) topognosis i.e., appreciation of the localization in space of the 

 point touched; (3) muscular sense; (4) stereognosis, or the power of 

 recognizing the form of objects touched and handled; (5) pain 

 e.g., that caused by a pin-prick; (6) volitional movement. The 

 postcentral gyrus in man appears to be the seat of a similar sensory 

 representation, but as its relation to the efferent impulses concerned 

 in volitional movements is less decided than that of the precentral 

 gyrus, so its relation to afferent impulses, both from the skin and the 



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