NO. I THE HYPOTROCHANTERIC FOSSA HRDLICKA 21 



(moderate), the juveniles a larger proportion of the medium forms, 

 which means that on the whole the fossa is better represented before 

 than in the adult stage. Some interesting conditions bearing on this 

 point will appear later in this paper. 



We find in the gorillas the hypotrochanteric fossa differing con- 

 siderably from that in the other anthropoid apes and especially from 

 that in man. It is generally spacious, oblique, at least partly marginal 

 (in the lateral border), situated low on the shaft — reaching in some 

 instances nearly to the middle— often shallow, and very decidedly 

 rougher than in man. There was found no marked extension of the 

 fossa over the lateral border onto the anterior surface. In four of the 

 pronounced cases the " fossa " was a marked groove. 



The frequency of the occurrence of the fossa in the older gorillas 

 is nearly the same as in the chimpanzees, but is less than in the orangs. 



The age differences are not so marked as they are in the orangs. 

 There is a mild diminution during the growth period of the " absents " 

 and " traces ", and but a slight increase in the more pronounced forms 

 of the fossa from adolescents to adults. On the whole, it may be 

 said that the fossa in the lowland gorilla increases moderately in 

 frequency as well as in development from childhood to adult life. 



In one adolescent left gorilla femur the hypotrochanteric fossa con- 

 sists of two superimposed hollows, the upper of medium, the lower of 

 submedium dimensions. There is no mistaking the second hollow for 

 Appleton's pectineal fossa or accessory adductor groove. 



The hypotrochanteric fossa in the gorilla, according to all the indi- 

 cations of its large rugose surface, gives attachment to a powerful 

 muscle — doubtless the gluteus maximus ; and the same must be true, 

 it would seem, of at least the more pronounced fossae in the orang 

 and the chimpanzee. In none of these forms is the gluteal ridge, 

 even when most distinct, of the human character and development. 

 Furthermore, neither in the gorillas nor in the orangs have I seen 

 any trace of a third trochanter; in the chimpanzees, though this 

 feature occurs in roughly 9 percent of the femora, it is never as 

 markedly developed as in some humans. It would seem to follow from 

 all this that the fossa plays a more important functional part in these 

 apes than it does in man ; in man, on the other hand, the gluteal ridge 

 and tuberosity (third trochanter) play the greater role. All this will 

 be considered further under the human materials. 



In the chimpanzees, the frequency of the fossa in children is much 

 less, in older subjects sHghtly less, than in the orang, and its charac- 

 teristics are slightly more like those in the human femur. None of the 



