1140 



HUMAN ANATOMY. 



cerebrum. It appears on each of the three aspects of the hemisphere and has, 

 therefore, a dorso-lateral, a mesial and an inferior surface. On the external surface 

 of the hemisphere it is bounded behind by the central fissure, which separates it from 

 the parietal lobe, and below by the fore-part of the Sylvian fissure, which intervenes 

 between it and the temporal lobe. On the mesial surface the frontal lobe includes 

 an irregular -> , marked off by the calloso-marginal sulcus, the longer upper limb 

 ending behind the central fissure. On the inferior surface of the hemisphere, the 

 frontal lobe includes the concave orbital area, bounded behind by the transversely 

 directed stem of the Sylvian fissure, which sulcus thus separates it from the temporal 

 lobe. 



The principal fissures on the dorso-lateral surface of the frontal lobe are: ( i ) the 

 inferior precentral, (2) the superior precentral, (3) the superior frontal and (4) the 

 inferior frontal. The inferior precentral sulcus consists of a longer vertical and 

 a short transverse limb and has a general ~| or T form. The vertical limb begins 

 above the fissure of Sylvius and in front of the central fissure and extends upward 

 parallel to the latter and separated from it by the lower part of the precentral 



convolution. The horizontal limb 

 passes obliquely forward and upward 

 and cuts for a variable distance into 

 the middle frontal convolution. Fre- 

 quently the inferior precentral sulcus 

 is directly continuous with the inferior 

 frontal furrow; sometimes it opens 

 below into the Sylvian fissure and 

 above may join the superior. 



The superior precentral sul- 

 cus prolongs upward the anterior 

 boundary of the precentral convolu- 

 tion. It lies parallel with the upper half 

 of the Rolandic fissure, but does not 

 usually, although sometimes reach the 

 upper margin of the hemisphere. Al- 

 most constantly it receives the poste- 

 rior end of the superior frontal sulcus 

 with which it forms a | shaped furrow. 

 The superior frontal sulcus 



FIG. 985. 



Anterior aspect of cerebral hemispheres, hardened in 

 skull; sf, i/, superior and inferior frontal fissures; /;., 

 paramedian; in.f, mid-frontal; /-/., fronto-marginal. 



extends forward from the preceding 



fissure with a course which corresponds in general with the supero-mesial border 

 of the hemisphere and thus marks off a longitudinal marginal tract, the superior 

 frontal convolution. Anteriorly the superior frontal may join the median frontal 

 sulcus, while its posterior end may incise the precentral convolution. Often the 

 course of the fissure is interrupted by superficial annectant gyri which connect the 

 adjacent borders of the upper and middle frontal convolutions. 



The inferior frontal sulcus begins behind in the interval between the hori- 

 zontal and vertical limbs of the inferior precentral furrow, or in confluence with one 

 of these. In its general course it arches forward and downward towards the anterior 

 <>r superciliary margin of the hemisphere and terminates a short distance behind 

 this border by bifurcating into a transverse limb. The line of the fissure is often 

 obscured by superficial annectant gyri and complicated by small secondary furrows 

 which pass from it into the bordering middle and inferior frontal convolutions. 



The convolutions on the dorso-lateral surface of the frontal lobe are the pre- 

 central, the superior frontal, the middle frontal and the inferior frontal. 



The precentral gyrus ( yrus contrails anterior), also known as the ascending 

 jiontnl, is bounded behind by the central fissure and in front by the superior and 

 inferior pmvntral sulci. Below it is limited by the Sylvian fissure, whilst its upper 

 end is continuous with the paracentral lobule of the mesial surface. Anteriorly it is 

 connected with all three frontal convolutions. A short distance above its middle, it 

 sends backward a conspicuous projection, triangular or rounded in outline, which 

 encnui lic^ upon the postcentral gyrus and correspondingly modifies the line of the 



