306 N. W, INGALL8 



the general arrangement of the sulci under consideration, the near- 

 est approach to the Gibbons being found in Semnopithecus. 



Passing to the lowest of the Simiidae, Hylobates (figs. 8-10), a 

 distinct advance and increase in complexity are at once noted, 

 and indeed the conditions in the Gibbon are essentially those 

 found in the other Simiidae, Chimpanzee, Orang and Gorilla. 

 The following account of the morphological arrangement in Hylo- 

 bates may be taken as representing the general pattern on which 

 also the corresponding area in higher forms and in man has been 

 modelled. The increased development of certain cortical regions 

 has placed the brain of the Anthropoids above that of all the 

 other Apes and similar lines of progress have raised above all the 

 brain of man. 



The fissura Sylvii has taken here a rather more horizontal 

 position and at the same time its length has decreased; possibly 

 it may be slightly shorter on the left side. Its posterior end is 

 variable : it may lie directly in the continuation of the rest of the 

 fissure, but more commonly shows some tendency to branch, 

 often into a typical arrangement of ascending and descending 

 limbs, or it may turn upward for a short distance. A posterior 

 subcentral is not infrequently present and may unite with the 

 Sylvian. Indications of transverse temporal gyri are often found. 



The sulcus temporalis superior is still a long and uniformly deep 

 furrow. It gradually approaches the Sylvian and sweeps round 

 it, in a very distinct curve, upward or even forward. Its course 

 may be somewhat irregular from the presence of interlocking 

 gyri in its walls, particularly just before it turns upward, at which 

 point a descending branch is not uncommon. The upturned end 

 of the sulcus is subject to some little variation. It may be 

 branched or not, and its location in the inferior parietal lobule 

 may vary. Both these conditions and the presence of the smaller 

 sulci in this region are often compensatory in character and closely 

 associated with, and due to, changes taking place in this area. 



The sulcus centralis is, as far as we are concerned, unchanged. 



The sulcus temporalis medius is present in the form of a few 

 irregular furrows disposed in general parallel with the superior 

 sulcus and of which the posterior furrows show a greater tendency 



