38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



the growth period ; and the second, what causes its regression during 

 adult life. 



The first question cannot be fully solved until we know precisely 

 what the fossa in man serves for. A portion of the development of the 

 fossa in size is possibly conditioned simply by the general growth of 

 the bone, though with a feature of this nature such a process may 

 not be as simple as it would seem at first thought. A more plausible 

 and appealing theory is that the fossa, during the growth period and 

 especially in adolescence, is functional but that it loses its value in this 

 respect during adult life. No definite conclusions on these points are 

 now possible; they can be reached only by extended observations on 

 suitable dissecting-room materials which thus far, notwithstanding 

 my efforts in this direction, could not be realized. 



The second problem, or what causes the curious regression of the 

 fossa during adult life, is also an involved one. There is the weakening 

 functional cause, of which very little can now be said ; and there is 

 the actual process of diminution-to-disappearance of the fossa in many 

 cases, which ought to be subject to observation. 



As a matter of fact, all the stages of a gradual occlusion of the 

 fossa may be witnessed in human femora, and in some cases such an 

 occlusion starts far ahead of the adult life. Occasionally as early 

 as the later childhood a more or less noticeable " deposit " of bone 

 may be observed in the upper part of the fossa. The process begins 

 as a rule in this upper part of the hollow and often in the form of 

 one or two isolated narrow vertical patches. Where it is larger, such 

 a " deposit " looks not osteophytic, but like a flow of some originally 

 viscid substance, or as if made by the pastry-makers' cone. As age 

 progresses, such " deiwsits " in the hypotrochanteric fossa become 

 slowly more frequent and more pronounced, and some of them may 

 clearly be seen to connect with and augment the gluteal ridge, whereas 

 in other cases they come to represent a gluteal tuberosity or third 

 trochanter. As the process is followed into the adult life, it is 

 possible to note all stages of obliteration of the fossa by these secon- 

 dary bony deposits, until in many instances only a small groove or 

 mere trace remains of the once well-marked hollow, and not infre- 

 quently the hollow disappears altogether, being traceable only by the 

 new bone formation. The fossa is thus encroached upon and more or 

 less assimilated by the progressive development of the gluteal ridge 

 and the need for a larger basis for the gluteal insertion. 



Before this peculiar encroachment and assimilation begin, the fossa 

 in the human femur is in general free from excrescences or irregu- 

 larities that would denote the attachment of a powerful muscle. It 

 is fusiform, symmetrical, and fairly smooth, with few exceptions in 



