30 SURGICAL APPLIED ANATOMY. [Chap. in. 



it, being a little less than two inches behind the 

 suture above, and a little more than one inch behind 

 it below. 



The temporo-sphenoidal lobe lies below a line drawn 

 horizontally backwards from the external angular 

 process. To find Broca's convolution (the posterior 

 part of the third left frontal convolution), a horizontal 

 line is drawn backwards from the external angular 

 process for two inches. The convolution is three- 

 quarters of an inch above the end of this line. The 

 upper borders of the optic thalamus and corpus 

 striatum are about on a level with the top of the 

 pinna. They are situate opposite the temporal region, 

 and the anterior limit of the corpus striatum about 

 corresponds to the pterion. 



The motor centres on the cortex. As an 

 aid to the localisation of certain lesions of the brain, 

 and as a means of explaining certain phenomena 

 when the cerebral cortex is damaged, a knowledge of 

 the cortical motor centres is most important. As 

 investigators do not agree entirely as to the exact 

 position of these centres upon the human brain, the 

 " cerebral localisation " of the principal authorities on 

 this subject is here given together without comment. 

 According to Charcot, (1) centre for movements of the 

 tongue, at the posterior end of the third frontal 

 conv. and contiguous part of the asc. frontal coiiv. ; 

 (2) centre for movements of lower part of face, at the 

 lower end of the two ascending convolutions ; (3) 

 centre for fore-arm and hand, on the middle third 

 of the asc. frontal conv. ; (4) centre for movements 

 of the lower limb, on the upper third of the asc. 

 frontal conv. and upper two-thirds of the asc. par. 

 conv. According to Hitzig, (1) motor centre for 

 upper limb, at upper part of asc. frontal conv. ; 

 (2) motor centre for lower limb, on asc. frontal 

 coiiv., just below preceding centre ; (3) motor centre 



