THE FKONTAL EEGION. 665 



superior lobule by the sulcus parietalis superior and the precuneus by the sulcus 

 prascunei (Fig. 589). 



The latter sulcus usually joins a small inverted U-shaped furrow (sulcus sub- 

 parietalis), which encloses a cortical territory of distinctive structure the area 

 parasplenalis [praecunei]. 



The inferior parietal lobule, which from its position is the natural meeting- place 

 for impressions coming from the visual, acoustic, and tactile territories, is naturally 

 a region of great functional significance. It is composed of a series of areas differ- 

 ing in thickness and texture. The anterior region forms a convolution (gyrus 

 supramarginalis) surrounding the upturned extremity of the lateral fissure ; behind 

 it there is a second convolution called the gyrus angularis, which surrounds a 

 vertical sulcus angularis, often described as the extremity of the sulcus temporalis 

 superior ; but in reality it is quite independent of the latter furrow, but it often 

 becomes confluent with it. Behind the gyrus angularis and separated from it by a 

 transverse furrow (sulcus occipitalis anterior) there is a cortical territory (area parieto- 

 occipitalis) which may perhaps be looked upon as a specialised and outlying part 

 of the peristriate area of the visual cortex. 





THE FKONTAL EEGION. 



The frontal region is the biggest of the main cortical areas the so-called "lobes." 

 On the lateral surface of the hemisphere, it is bounded behind by the sulcus centralis 

 and below, in part, by the lateral fissure. It presents a lateral surface, a medial 

 surface, and an inferior or orbital surface. 



On its lateral aspect the surface is broken up by a large series of furrows, 

 which exhibit considerable variability. 



The inferior precentral sulcus consists of a vertical and an oblique part. The 

 vertical portion lies in front of the inferior part of the sulcus centralis, whilst 

 the oblique part extends forwards and upwards (Fig. 594). 



The superior precentral sulcus is a short vertical sulcus which lies at a higher 

 level than the inferior precentral sulcus, in front of the upper part of the sulcus 

 centralis. It is almost invariably connected with the posterior end of the superior 

 frontal sulcus. 



The anterior central gyrus is a long continuous gyrus, which is limited in front 

 by the two precentral furrows and behind by the sulcus centralis. Inferiorly it is 

 continuous with the area subcentralis which links it to the posterior central gyrus. 

 The area subcentralis is limited in front and behind by the anterior and posterior 

 sulcentral sulci (not labelled in Fig. 594). 



The superior frontal sulcus extends forwards in a more or less horizontal direc- 

 tion from the sulcus praecentralis superior. 



The gyrus frontalis superior is the narrow convolution between the supero-medial 

 border of the hemisphere and the superior frontal sulcus and the continuation of 

 this convolution into a broad area upon the medial surface. 



The inferior frontal sulcus occupies a lower level than the superior frontal sulcus. 

 Its posterior end is placed in the angle between the vertical and horizontal parts of 

 the inferior precentral sulcus, and is not infrequently confluent with one or other 

 of these. It proceeds forwards towards the superciliary margin of the hemisphere 

 and ends a short distance from this in a terminal bifurcation (Fig. 594). 



The gyrus frontalis medius is the name given to the broad convolution which 

 lies between the superior and inferior frontal sulci. 



The gyrus frontalis inferior is that portion of the lateral surface of the frontal 

 region which is placed in front of the inferior precentral sulcus and below the 

 inferior frontal sulcus. The inferior frontal convolution includes three cortical 

 areas (Fig. 594) differing in structure the one from the other. The sulcus diagonalis 

 separates the intermediate of these from the posterior. 



The sulcus frontalis medius begins midway between the anterior ends of the 

 superior and inferior frontal sulci and proceeds obliquely forwards towards the 

 frontal pole. When the furrow reaches the superciliary margin of the hemisphere 

 it ends near a transverse furrow, called the fronto-marginal sulcus. 



