4io THE BRAIN 



and they run parallel with the central sulcus, from which 

 they are separated by the posterior central gyrus. Not un- 

 commonly, the two post-central sulci are continuous with 

 one another in the adult ; and either the one or the other may 

 be continuous with the sulcus interparietalis proprius (Figs. 



152, 155)- 



Sulcus Interparietalis Proprius. The interparietal sulcus 

 proper runs backwards, almost horizontally, about midway 

 between the upper and lower borders of the supero-lateral 

 surface of the parietal lobe. It separates the superior from 

 the inferior parietal lobule, and it may be continuous, anteriorly, 

 with one or other of the post-central sulci, and, posteriorly, 

 with the par-occipital sulcus. 



Sulcus Paroccipitalis. In the adult, the par-occipital sulcus 

 is either directly continuous with, or it commences close to, 

 the posterior end of the sulcus interparietalis proprius. It 

 runs backwards, past the lateral end of the parieto-occipital 

 fissure, from which it is separated by a parieto-occipital 

 annectant gyrus called the arcus parieto-occipitalis ; and it 

 terminates, in the occipital lobe, in the transverse occipital 

 sulcus (Figs. 137, 152, 154). 



In the past it was the custom to speak of an interparietal sulcus which 

 consisted of a vertical, a horizontal and an occipital portion. The vertical 

 part is the inferior post-central sulcus, the horizontal part is the sulcus 

 interparietalis proprius, and the occipital part is the par-occipital sulcus. 



The Gyri of the Supero-lateral Surface of the Parietal Lobe. 

 The subdivisions of the supero-lateral surface of the 

 parietal lobe are the posterior central gyrus ; the superior 

 parietal lobule ; and the supra-marginal, the angular, and the 

 post-parietal gyri, which form collectively the inferior parietal 

 lobule (Fig. 152). 



Gyrus Centralis Posterior. The posterior central gyrus lies 

 between the central and the post-central sulci. Along its 

 anterior face, which forms the posterior wall of the central 

 sulcus, and along the adjacent part of the supero-lateral surface 

 lies the main area of ordinary sensation (Fig. 153). It is 

 continuous, above and below, with the anterior central gyrus, 

 and posteriorly with the superior and inferior parietal lobules. 



Lobulus Parietalis Superior. The superior parietal lobule 

 is bounded, anteriorly, by the superior post-central sulcus ; 

 posteriorly, by the parieto-occipital fissure ; above, by the 

 supero-medial border ; and, below, by the sulcus interparietalis 



