236 THE NERVOUS SYSTEM 



temporal lobe which terminates rostrally in the temporal pole. The superior 

 temporal sulcus is a very constant fissure, which begins near the temporal pole 

 and runs nearly parallel with lateral cerebral fissure. Its terminal part turns 

 dorsally into the parietal lobe. The middle temporal sulcus, ventral to the pre- 

 ceding and in general parallel with it, is usually composed of two or more dis- 

 connected parts. The inferior temporal sulcus is located for the most part on 

 the basal surface of the temporal lobe. Dorsal to each of these fissures is a 

 gyrus which bears a similar name: the superior temporal gyrus, between the 

 lateral fissure and the superior temporal sulcus; the middle temporal gyrus, be- 

 tween the superior and middle temporal sulci; and the inferior temporal gyrus, 

 between the middle and inferior temporal sulci. The lateral fissure is very deep ; 

 and the surface of the superior temporal gyrus that bounds it is broad and marked 

 near its posterior extremity by horizontal convolutions, known as the transverse 

 temporal gyri. One of these, more marked than the others, has been called the 

 anterior transverse temporal gyrus or Heschl's convolution and represents the 

 cortical center for hearing (Fig. 174). 



The Parietal Lobe. The postcentral sulcus runs nearly parallel with the 

 central sulcus and consists of two parts, the superior and inferior postcentral 

 sulci, which may unite with each other or with the inter parietal sulcus. Often 

 all three are continuous, forming a complicated fissure, as shown in Fig. 168. 

 The interparietal sulcus extends in an arched course toward the occiput and 

 may end in the transverse occipital sulcus. These four sulci are often included 

 under the term "interparietal sulcus." The interparietal sulcus proper is then 

 designated as the horizontal ramus. 



The posterior central gyrus lies between the central and postcentral sulci. 

 The interparietal sulcus separates the superior parietal lobule from the inferior 

 parietal lobule. Within the latter we should take note of two convolutions: 

 the supramarginal gyrus, which curves around the upturned end of the lateral 

 fissure; and the angular gyrus, similarly related to the terminal ascending por- 

 tion of the superior temporal fissure. 



The Occipital Lobe. Only a small part of the dorsolateral surface of the 

 hemisphere is formed by the occipital lobe. This is a triangular area at the 

 occipital extremity, bounded rostrally by a line joining the parieto-occipital 

 fissure and the preoccipital notch (Fig. 167). The transverse occipital fissure 

 may help to bound this area or may lie within it. Other inconstant sulci help 

 to divide it into irregular convolutions. Sometimes the visual area which lies 

 on the mesial aspect of this lobe is prolonged over the occipital pole to the lateral 



