310 N. W. INGALLS 



Although fashioned on the same general plan as found in the 

 Gibbons, there is in all the other Anthropoids a very great increase 

 in complexity and variability of detail. Among the essential dif- 

 ferences, advances, may be mentioned the followung points, a 

 general discussion of which will be entered into later (fig. 11). 



The fissura Sylvii is more horizontal and relatively shorter, 

 its borders are much indented, either from the transverse sulci 

 of the opercula or from its union with neighboring sulci; its pos- 

 terior end is in particular variously branched and either separate 

 or united to the sulci of the supermarginal gyrus. 



The parallel sulcus still preserves in a measure what we may 

 call its primitive form in that it extends from the temporal pole 

 almost to the interparietal. It has suffered, however to some ex- 

 tent in that its course is less regular, there being frequent inden- 

 tations of its walls and interlocking gyri. At its posterior ex- 

 tremity it is usually markedly branched and irregular and as 

 it turns around the Sylvian it very commonly has a deep branch 

 directed downward and backward; a ramus descendens. Its pos- 

 terior third may be quite independent, as a sulcus angularis. 



There have been no very radical changes in the second temporal 

 sulcus, but there is the tendency for it to form a continuous fur- 

 row. Its posterior end may be in relation with a Querfurche, 

 confluent with the inferior occipital or independent, sometimes 

 turning abruptly upward. 



Although the sulcus lunatus is still a conspicuous feature, it 

 lacks the regularity and constancy of form and position which 

 it exhibits in the lower primates. Relatively smaller, it is also 

 placed nearer the occipital pole and the mesial extremity has re- 

 treated more than in the lateral, especially in Gorilla and Orang, 

 so that viewed from behind its direction approaches the hori- 

 zontal and a portion at least of the posterior limb of the first an- 

 nectant gyrus is exposed. The prelunate is much like that in 

 Gibbon. 



A paramesial sulcus may be present, especially in Gorilla, on 

 account of the retraction of the mesial end of the lunate. 



As regards the interparietal system, the conditions in the Orang 

 and Gorilla are most like those in the Gibbon, while in the Chim- 



