36 APPLIED ANATOMY. 



or contraction of the muscles connected with it, and is the region most frequently 

 affected by injuries. This is partly due to the fact of its proximity to the middle 

 meningeal artery, as a hemorrhage from that vessel produces a clot which covers 

 and involves this area. 



The Rolandic area embraces the ascending frontal, or precentral, and posterior 

 portion of the three frontal convolutions, the former being in front of the fissure 



FIG. 44. Diagram illustrating the motor areas of the lateral surface of the brain. 



of Rolando, or central fissure. The fissure of Rolando passes downward and for- 

 ward from the longitudinal fissure, at an angle of about 70, nearly to the fissure of 

 Sylvius, being separated from it by the joining of the ascending parietal and ascend- 



FIG. 45. Diagram illustrating the probable functions of the gyri (convolutions) of the medial surface of the brain. 



ing frontal convolutions. Sherrington and Griinbaum have shown that the motor 

 area is almost exclusively anterior to the central fissure. 



The upper portion of the motor area, near the longitudinal fissure, is concerned 

 with the movements of the toes and lower extremity. The leg centres are toward 

 the upper end of the central fissure; next are those of the abdomen and chest. 

 The arm centres are toward the middle, and the face centres, including the larynx, 



