856 A MANUAL OF PHYSIOLOGY 



lysis of the muscles, or rather movements, represented in the 

 area supplied by it. A tumour causes symptoms of irritation, 

 motor or sensory convulsions beginning in, or sensations 

 referred to, the parts represented in the regions on which it 

 presses. In connection with the localization 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 post- 

 central 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 protuberance 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 longitudinal fissure (Fig. 355). 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 embryo- 

 logical 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. 850), removal of the 

 Rolandic cortex causes defects of sensation as well as of move- 

 ment. 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 convolution), 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 limb 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 recognising 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 



