THE BRAIN. 



35 



produced by an injury to the path leading from those centres, the motor tract as it 

 is called, by a hemorrhage, as from apoplexy, involving the corresponding white 

 matter fibres. 



The exact localization of the functions of all parts of the brain has not been 

 accomplished, but the functions of many areas have been definitely proven. In 

 cases of brain tumor, abscess, hemorrhage, injury, etc. , a knowledge of these areas 

 enables one to localize the seat of the lesion. 



FUNCTIONS OF THE CONVOLUTIONS ON THE SURFACE OF THE CEREBRUM. 



The frontal lobe may be conveniently divided into three areas; prefrontal, mid- 

 frontal, and postfrontal. The prefrontal area embraces all the superior, middle, 

 and inferior frontal convolutions, with the exception of their posterior ends. On 

 the medial side it reaches to the callosomarginal fissure. The function of the pre- 

 frontal area is said to be that of higher cerebration, as attention, judgment, and com- 

 parison. This region, particularly the lower portion, is liable to injury, owing to its 

 anterior position and to the fact that it overlies the orbit. The roof of the orbit is 

 quite thin and liable to fracture by penetrating bodies, as umbrellas, canes, etc. 

 Sometimes a portion of this part of the brain may be destroyed without marked 

 interference with the mental qualities of the patient. This occurred in the case of a 



Fig. 43. 'Diagram illustrating the probable functions of the lateral surface of the brain. 



boy who was struck in the eye by a carriage pole (personal observation). The eye 

 was burst, necessitating its removal. Several pieces of the fractured bone of the 

 roof of the orbit were removed and brain tissue came away for several days. The 

 boy recovered and for sixteen years apparently had no resulting mental deficiency. 



The midfrontal area embraces the posterior portion of the superior and 

 middle convolutions, with the upper posterior portion of the inferior. It is con- 

 cerned in certain movements of the eyes and lids, and also in turning the head 

 toward the opposite side. This midfrontal division is the most anterior portion of 

 what is called the motor area. 



Speech Centre, or Broca's Convolution. The centre of speech is located 

 in right-handed people in the posterior portion of the third left frontal convolution, 

 where it arches around the ascending limb of the fissure of Sylvius. It is called 

 Broca's convolution. The faculty of writing or written speech is attributed to the 

 graphic centre in the posterior extremity of the second frontal convolution just above 

 and behind Broca's convolution. 



The postfrontal area embraces the ascending frontal convolution in front of 

 the fissure of Rolando or central fissure. It is concerned in the various movements 

 of the trunk and extremities, and forms the anterior portion of the Rolandic area; 

 it will be considered under that head. 



The Rolandic Area. This is the area which gives rise to most of the voluntary 

 movements of the body. When affected, it causes positive symptoms of paralysis 



