NO. 8 HISTOLOGY OF THE FEMUR — FOOTE J 



units are not at all common below mammals, but are the important 

 structures of mammals and especially man. 



MAN 



The human fetus presents in varying combination the first and 

 second type of structure with wide canals and incompletely formed 

 lacunae. As development progresses, the first and second type bone 

 is gradually displaced by the Haversian system structure. 



More in detail, in the very young human fetus of two to three 

 months, the first type of bone structure is present in an incomplete 

 form and is marked off into irregular areas by crude, branching 

 canals. As fetal life advances the canals become less branching and 

 more concentric. Gradually the first becomes the second type of 

 bone and remains so until about one year after birth, when sufficient 

 differentiation has occurred by the formations of Haversian systems 

 to make it second and third type, or first, second and third type com- 

 bination. Throughout childhood and youth, the laminae tend to dis- 

 appear and to be replaced by Haversian systems, until the bone devel- 

 opment is completed. In the early period, a horseshoe-shaped band 

 of laminae is often observed forming the anterior and lateral walls of 

 the bone. A remnant of this horseshoe may remain throughout life 

 in those femora which do not complete the third type differentiation. 

 The proportion of this remnant to the other bone units in the adult 

 bone varies greatly and the result is that adult femora present many 

 secondary variations. 



A white child, a Pueblo Indian, and a Peruvian Indian child, each 

 about one year of age, exhibited already a combination of the second 

 and third types of bone structure. A femur of an Egyptian child of 

 the Xllth Dynasty showed the development of the Haversian system 

 directly from the circulation, which is an evidence of the causal asso- 

 ciation of bone structure with the development of the vascular system 

 of the bone. 



On the whole, the study of human femora from fetal life and child- 

 hood shows various transitional stages from the first and second to the 

 third type of bone. 



ADULT HUMAN FEMORA 

 The adult human femora are, in general, characterized by the pre- 

 dominance of a well differentiated third type of structure. An 



