NO. I THE HVPOTROCHANTERIC FOSSA IIRDLICKA 47 



The hypotrochanteric fossa in man is a well-established phyletic 

 feature passed on from the common ancestry of man and of the 

 larger anthropoid apes. It is a feature the old function of which, 

 apparently, was that of a place for the attachment of the gluteus 

 maximus; but in man this function has it seems become largely, if 

 not entirely, obsolete, and in part perhaps changed. 



Ontogenetically, the fossa begins to appear from the fifth month 

 of the intrauterine life; but because of its lost importance, in all 

 probability, there is much retardation, so that the period during which 

 it may originate is greatly prolonged, extending over practically the 

 entire growth period. 



Doubtless for the same reason, i.e., the obsolescence of the fossa 

 in the human femur, there are cases in which the hollow does not 

 appear at all, and there are many in which it develops only in a more 

 or less rudimentary form. 



And from the same cause, basically, the fossa is not permanent. 

 On the whole, it reaches its optimum dimensions during adolescence, 

 but in individual instances even in childhood, it begins to show already 

 signs of obliteration. This obliteration is due to secondary bone 

 deposits or growths beginning in and extending from the upper 

 part of the fossa. It is a slowly progressive osteoblastic process 

 that finally involves and occludes most or all of the fossa and thus 

 leads to its partial or total disappearance. This regressive course, 

 although it may begin early, is essentially a phenomenon of the sub- 

 adult and adult periods and proceeds to old age. 



The active cause of this regression or obliteration is the gluteal 

 insertion adjacent to the fossa. This insertion in man has become 

 confined mainly or entirely to the gluteal ridge ; and in active in- 

 dividuals, as the need for a greater insertion grows, new bone that 

 eventually becomes assimilated into the enlarging gluteal ridge is 

 deposited, and this deposit is always realized in and at the expense of 

 the hypotrochanteric fossa. Thus the gluteal ridge during subadult 

 and adult life may be said to more or less assimilate the fossa. 



The hypotrochanteric fossa possesses some interesting physical 

 characteristics. From the start, when it is a mere imprint on the bone 

 rather than a hollow, it presents a well-demarked fusiform outline, 

 with the long axis vertical and always longer than the transverse. 

 The floor of the fossa, reticulated at first, becomes in general sym- 

 metrical and fairly smooth later on. In a small proportion of femora 

 the lower boundary of the fossa is wanting, and the hollow then 

 forms a marked smooth groove, which descends parallel with the 



