472 THE BRAIN 



parieto-occipitalis, it bifurcates into two widely spread-out 

 branches. These form a short transverse fissure in the 

 occipital lobe, termed the sulcus occipitalis transversus (Ecker) 

 (Fig. 1 86). 



The upturned ends of the posterior branch of the lateral 

 fissure, of the superior temporal sulcus and of the middle 

 temporal sulcus (Fig. 186) extend for a short distance, one 

 posterior to the other, into the inferior parietal lobule. 



Gyri on the Lateral Surface of the Parietal Lobe. The 

 interparietal sulcus maps out three districts or areas on the 

 lateral surface of the parietal lobe. These are the posterior 

 central gyrus and the superior and inferior parietal lobules. 



The gyrus centralis posterior (Fig. 186) is a long gyrus 

 which extends obliquely across the hemisphere from the supero- 

 medial border above to the posterior branch of the lateral 

 fissure below. Anteriorly, it is bounded by the central 

 sulcus, and posteriorly, by the superior and inferior postcentral 

 sulci. 



The superior parietal lobule is the area of cerebral cortex 

 which lies between the ramus horizontalis below and the 

 supero-medial border of the hemisphere above. It is bounded 

 anteriorly by the superior postcentral sulcus ; and posteriorly, 

 it is connected with the occipital lobe by the arcus parieto- 

 occipitalis. It is continuous around the supero-medial border 

 of the hemisphere with the praecuneus. 



The inferior parietal lobule lies below the ramus horizon- 

 talis and the ramus occipitalis, and posterior to the inferior 

 postcentral sulcus. It is more or less directly continuous 

 with the occipital lobe posteriorly and with the temporal 

 lobe below. It presents three arching gyri, viz. the supra- 

 marginal anteriorly, the post-parietal posteriorly, and the 

 angular between them. 



The supra-marginal gyrus (Fig. 186) is folded round the 

 upturned end of the posterior branch of the lateral fissure and 

 is continuous with the superior temporal gyrus. The angular 

 gyrus (Fig. 186) arches over the upturned end of the superior 

 temporal sulcus, and is continuous with the middle temporal 

 gyrus. The post-parietal gyrus (Fig. 186) winds round the 

 upturned end of the middle temporal sulcus, and runs into 

 the inferior temporal gyrus. 



Boundaries of the Occipital Lobe. The occipital lobe 

 forms the posterior pyramidal part of the cerebral hemi- 



