THE CEREBRUM 475 



Boundaries of the Temporal Lobe. The temporal lobe lies 

 posterior to the stem of the lateral fissure and below its 

 posterior branch. It presents an upper, a lateral, and a 

 tentorial surface, with a free apex or pole which projects 

 anteriorly. Above, it is bounded by the posterior branch 

 of the lateral fissure together with the artificial line drawn 

 posteriorly from that fissure. On the tentorial surface it is 

 separated from the hippocampal gyrus by the collateral fissure ; 

 whilst posteriorly, it is marked off from the occipital lobe by 

 the arbitrary lines described on p. 470. The apex or temporal 

 pole projects anteriorly on the under surface of the brain. 

 It should be noticed that the recurved extremity of the 

 hippocampal gyrus, which lies to the medial side of the 

 hemisphere, does not reach the temporal pole, but is 

 separated from it by the incisura temporalis or ectorhinal 

 fissure. 



Upper or Opercular Surface of the Temporal Lobe. This 

 is the surface of the temporal operculum which is opposed to 

 the insula and the fronto- parietal operculum. The lateral 

 fissure must therefore be widely opened up to expose it. 

 For the most part the surface is smooth, but towards its 

 posterior part there are a few shallow furrows, called the 

 sulci of Heschl) whilst anteriorly, also on the deep aspect of 

 the temporal pole, two or three furrows are evident. 



Lateral Surface of the Temporal Lobe. On this aspect of 

 the lobe there are two horizontal sulci, called the superior 

 and middle temporal sulci. 



The superior temporal sulcus (Fig. 186) is a long, continuous 

 and deep cleft which begins near the temporal pole and 

 proceeds posteriorly, below the posterior branch of the lateral 

 fissure. Its posterior end turns upwards, into the parietal lobe, 

 and is surrounded by the angular gyrus. 



The middle temporal sulcus is placed midway between the 

 superior temporal sulcus and the infero-lateral border of the 

 hemisphere. It is very rare to find it in the form of a con- 

 tinuous cleft. Usually it is broken up into several isolated 

 pieces, placed one posterior to the other. Its posterior part 

 turns upwards into the parietal lobe (Fig. 186), where it is 

 surrounded by the post-parietal gyrus, and lies close to the 

 artificial line of demarcation between the occipital and 

 parietal lobes. 



By these two temporal sulci the lateral surface of the 



