THE CEREBRUM 467 



central sulcus. It is almost invariably connected with the 

 posterior* end of the superior frontal sulcus. 



Gyrus Centralis Anterior. The anterior central gyms is a 

 long continuous gyrus which is limited anteriorly by the two 

 praecentral sulci, and posteriorly by the central sulcus. It 

 extends obliquely across the hemisphere, from the supero- 

 inedial margin above to the posterior branch of the lateral 

 fissure below (Fig. 186). 



Sulcus Frontalis Superior (Fig. 186). The superior frontal 

 sulcus extends anteriorly from the sulcus praecentralis superior. 



Gyrus Frontalis Superior (Figs. 186, 187). The superior 

 frontal gyrus lies above the superior frontal sulcus and passes 

 round the supero-medial border on to the medial surface 

 of the hemisphere. It terminates anteriorly in the frontal 

 pole. 



Sulcus Frontalis Inferior (Fig. 186). This lies at a lower 

 level than the superior sulcus of the same name. The posterior 

 end of the inferior frontal sulcus is placed in the angle 

 between the vertical and horizontal parts of the inferior 

 praecentral sulcus, and is not infrequently confluent with one 

 or other of these. It passes anteriorly towards the superciliary 

 margin of the hemisphere, and ends a short distance from 

 it in a terminal bifurcation. 



Gyrus Frontalis Medius (Fig. 186). The middle frontal 

 gyrus is the broad convolution which lies between the superior 

 and inferior frontal sulci. 



Gyrus Frontalis Inferior (Fig. 186). The inferior frontal 

 gyrus is that portion of the lateral surface of the frontal lobe 

 which is placed anterior to the inferior praecentral sulcus and 

 below the inferior frontal sulcus. 



The sulcus paramedialis is the term applied to a series of short 

 irregular furrows arranged longitudinally, close to the supero-medial border 

 of the hemisphere. These rudimentary sulci partially subdivide the superior 

 frontal gyrus into an upper and lower division, and are of interest in so 

 far that they are best marked in high types of brain. 



The middle frontal sulcus (Fig. 186) lies horizontally in the anterior part 

 of the middle frontal gyrus, and divides it into an upper and a lower 

 part (Fig. 186). As it approaches the superciliary margin of the hemi- 

 sphere it bifurcates, and its terminal branches spread out widely from each 

 other, and together constitute a transverse furrow called the sulcus fronto- 

 marginalis. 



Owing to the subdivision of the superior and middle frontal gyri in the 

 manner indicated, the gyri in the anterior part of the lateral surface of the 

 frontal lobe are arranged in five horizontal tiers. 



