THE PARIETAL AND OCCIPITAL CONVOLUTIONS. 751 



ascending frontal, and like that is simple, arid extends from the upper 

 margin of the hemisphere to the posterior branch of the Sylvian 

 fissure. In front of it is the furrow of Rolando, round the ends of 

 which it joins the ascending frontal convolution. Behind, it is 

 limited by the superior postcentral sulcus above, and the ascending 

 part of the intraparietal, or the inferior postcentral sulcus below. 



Parietal lobules. The larger portion of the parietal lobe behind superior 

 the ascending parietal convolution is divided into two parietal lobule, 

 lobules by the horizontal part of the intraparietal sulcus. The 

 ior parietal lobule (SPL) is connected in front to the upper end 

 of the ascending parietal convolution between the postcentral sulcus 

 and the upper margin of the hemisphere, and behind to the upper 

 occipital convolution by a small winding gyrus which is called the 

 lirst or superior parieto-occipital annectant convolution (below po). 

 This lobule is divided into several secondary gyri. 



The inferior parietal lobule is again subdivided into two, or some- and inferior 

 times three, convolutions, but the separation between them is often lobule, 

 very indistinct. The supramaryinal convolution (SM) is the anterior constating 

 and larger of these ; it springs in front from the lower end of the marginal, 

 ascending parietal convolution, encircles the extremity of the 

 posterior branch of the Sylvian fissure, and ends by joining the 

 first temporal convolution. 



The angular convolution (Any] arises from the hinder part of the angular, 

 foregoing, arches over the upper end of the first temporal sulcus (st) 

 and descends behind that furrow to be continued into the second 

 temporal convolution. 



A third part of the inferior parietal lobule may also be dis- and post- 

 tinguished, but it is not indicated in fig. 270. It is called the convoki- 

 post-parietal convolution, and is continuous with the angular convolu- tions. 

 tion in front. It arches over the up-turned end of the second 

 temporal sulcus, in front of which it is continuous with the second 

 and behind with the third temporal convolution. Posteriorly 

 also it is continued into the occipital lobe and forms the inferior 

 parieto-occipital annectant convolution. The posterior part of the 

 second temporal sulcus, which it embraces, is often separate from 

 the anterior part of that sulcus, and can only be distinguished from 

 the latter by the fact that it continues the direction of the furrow 

 backwards and upwards. 



SOLCI AND CONVOLUTIONS OF THE OCCIPITAL LOBE. The occipital Occipital 



lobe is divided into three convolutions, which run forwards from convolu^ 

 the posterior extremity of the hemisphere, by two small furrows tions are 

 the superior and middle occipital sulci. The superior occipital convolu- nmSle^and 

 tion (so) is united anteriorly to the superior parietal lobule by the inferior - 

 superior annectant gyrus ; the middle (MO) to the post-parietal con- Annectant 

 volution by the inferior, and the inferior (10) to the third temporal 

 convolution by the occipito-temporal annectant gyrus. An inconstant 

 inferior occipital sulcus, at the lower margin of the hemisphere, 

 separates the third occipital convolution from the temporal lobe on 

 the under surface. The occipital convolutions are very variable, 

 and the sulci are frequently ill marked. 



