NO. I THE HYPOTROCHANTERIC FOSSA IIRDLICKA IQ 



THE FOSSA IN ANTHROPOID APES 



Conditions as to the hypotrochanteric fossa in the anthropoid apes, 

 aside from the gibbons and sianiangs, are widely different from those 

 of the lower apes; but the forms differ also considerably infer se, 

 as well as from humans, but in other respects. The gibbons approach 

 the monkeys, as they do in so many other characters. 



The results of the observations will be seen in the table on page 20. 



The gibbon femora, it is seen, have not even a trace of the hypo- 

 trochanteric fossa in nearly 86 percent of those examined, and in but 

 two among the five bones with the fossa is it at all fairly developed. 

 However, where the fossa is present, it approaches the human type, 

 though it is more marginal ; and in the bone in which it is best de- 

 veloped it presents a new feature— it is a groove without lower (distal) 

 boundary, and not a circumscribed fossa. This is a feature that has 

 not hitherto been reported, but one with which we shall meet again 

 in these reports. 



The gluteal ridge in these gibbons is either absent or ranges in 

 development up to fairly well pronounced. There is no third 

 trochanter," 



Among the three large anthropoid apes, the hypotrochanteric fossa 

 is most frequent in the orang and least so in the chimpanzee, but in 

 all three genera its presence is relatively common. This is so striking 

 in contrast with the lower apes that the fossa, as far as the order 

 of the primates is concerned, may henceforth justly be regarded as. 

 essentially a higher-anthropoid, and, as will be seen later, also human, 

 character. 



In the orangs the fossa is almost universal, though not often very 

 pronounced. It is as a rule more or less marginal, i.e., partly or 

 wholly in the lateral border. In two pairs of the femora, one from 

 Borneo and one from Sumatra, the fossa is displaced entirely to the 

 lateral part of the anterior surface, and in one other Sumatra orang 

 femur there is a partial displacement of such a nature. This com- 

 plete or partial displacement 0*f the hypotrochanteric fossa is another 

 feature that has not been reported before, but its reality is unquestion- 

 able. (See pi. 4.) 



The differences in the incidence and character of the fossa between 

 the juvenile and adult femora in the orangs is obscured by the in- 

 sufficiency of the number of specimens for such a comparison; never- 

 theless, the adults show clearly a larger proportion of the submedium 



" Observations on these formations were recorded in every case and will be 

 dealt with more in detail in a separate article. 



