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 prefrontal area is said to be that of higher cerebration, as attention, judgment, and comparison. 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 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.

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

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

The midfrontal area embraces the posterior portion of the superior and middle convolutions, with the upper posterior portion of the inferior. It is concerned 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 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 of Rolando, or central fissure. The fissure of Rolando passes downward and forward from the longitudinal fissure, at an angle of about 700, nearly to the fissure of Sylvius, being separated from it by the joining of the ascending parietal and ascending frontal convolutions. Sherrington and Grunbaum have shown that the motor area is almost exclusively anterior to the central fissure.

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

Fig. 44. - Diagram illustrating the motor areas of the lateral surface of the brain.

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

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

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.

tongue, and platysma myoid muscle, around its lower extremity. The leg, arm, and face centres are, respectively, opposite the posterior extremities of the superior, middle, and inferior frontal convolutions.

The upper portion of the motor area passes over the upper margin of the hemisphere and down on its medial side almost as far as the callosomarginal fissure and paracentral lobule.