NO. 3 COMPARATIVE HISTOLOGY OF KBMUR FOOTE 31 



shoe shape iirouud the medullary t-aiial. The systems were composed of bone 

 substance with oval and long lacuua3 and with bushy and straight canaliculi. 

 They gaxe one the impression of Haversian systems very mucli flattened by 

 pressure. The posterior ridge or linea aspera, clea'rly distinct and wider than 

 in the foregoing sections, was composed of elongated Haversian systems, and 

 was divided into two lateral halves by a narrow radiating space, which is the 

 last part of the linea aspera to become bone (pi. 21, fig. 303). 



In a series of five Pueblo Indian femora of different ages, from one year to 

 adult age, various further developmental stages were shown (pi. 9, figs. 341- 

 344). The cliild's femur was composed of incompletely developed laminfe and 

 Haversian systems, the systems ranging from the (la) to the (C) differentia- 

 tion. The posterior ridge, only partly formed in the femur of one year, was 

 much further advanced in the femur of six years. In the femur of early youth 

 the lamiuas were, to a considerable degree, displaced by incompletely developed 

 Haversian systems, and the posterioi- ridge could not be distinguished from 

 the lateral wall. In the femur of later j^outh the Haversian systems have 

 increased in proportion and advanced markedly in development, and in the 

 adult bone the lamelte and lamina; were almost entirely displaced by fuUy 

 developed Haversian systems. While these femora were from different in- 

 dividuals and probably from individuals of unlike types; yet they sliowed, in a 

 general way, the differentiating changes in bone development. The Chicama 

 and Pachacamac Indians showed similar changes. 



Reviewing the above differentiations chronologically, evidences of advance- 

 ment were strikingly apparent with increase in age. The femur of the human 

 fetus begins its osseous history as a bone of crude first type, and then gradually 

 advances through the second to the pure third type, or to some combination 

 of the first and third, second and third, or first, second, and third types. Ha- 

 versian systems begin with the most primitive, incomplete, and advance to the 

 fully developed stage, gradually increasing at the same time in number. An 

 early twofold division of the femoral wall increases to a threefold division. 



It may also be seen that the linea aspera of the human femur is the 

 product of a distinct bone formation which occurs in the posterior wall. It 

 was noticed at the early age of three and one-half months, and was observed in 

 the different femora until birth. Therefore, in the formation of the shaft of 

 the human femur, two distinct bone forming processes seem to be evident, one 

 the formation of the liorseshoe-shaped band of the anterior and lateral walls, 

 and the other of the posterior ridge or linea aspera. They appear to go on 

 independently of each other for a while, and fuse together some time after birtii. 



The development of the linea aspera — tlie last part of the shaft to be com- 

 pleted — is especially interesting from the viewpoint of its function and tlie 

 growth of bone. 



