isro. 3 



COMPARATIVE HISTOLOGY OF FEMUR FOOTE 



23 



proportionately a smaller percentage of bone substance than the femora of 

 other races (pis. 25-27, figs. 341-361). 



Egyptian femora of the twelfth dynasty. — This series includes the femora 

 of children, youth, and adults. The bones are interesting on account of their 

 antiquity. They show the structure of the femur of four thousand years ago. 

 By comparing them with modern femora it will be seen that the bone types 

 which were prominent then are still prominent now. 



One of the most interesting femora examined was that of a young child, 

 figures 363 and 363-a. It showed the formation of an Haversian system from 

 the circulation, an account of which will be found elsewhere (p. 177). Two or 

 three femora from adolescents showed gradually diminishing first and second 

 and increasing third type units. The adult bones showed two main types of 

 differentiation. One was composed of lamella? enclosing Haversian systems, 

 and the other of Haversian systems alone, figures 369 and 370. Femur 369 

 bears the stamp of a much lower degree of development than femur 370. Femur 

 369 was much more than half lamella 3 , while 370 was composed entirely of 

 Haversian systems (pis. 27-28, figs. 363-371). 



The white race. — The femora of the modern white race showed a variety 

 of type combinations as well as single types. On the whole, the complete Ha- 

 versian system type predominated. A larger percentage of the bones examined 

 than in any other race showed the third type structure and senile changes. 

 Individual differences in structure were quite extensive. 



The average medullary index, as already seen, was 35.8%. That is, the 

 femur of the white race had a smaller medullary canal and thicker wall of bone 

 than the femur of the other races. In the III, C type of femora the Haversian 

 systems varied considerably in size. Some were small with a few, while others 

 were large with many, concentric lamellae. The communicating canals between 

 the systems also varied greatly. In some femora they were very numerous and 

 provided a rich blood supply for the whole bone ; in other femora they were few 

 in number, comparatively, and the Haversian circulation was very much dimin- 

 ished. Differences in the extent of the circulation in different parts of the bone 

 were observed. The inner wall generally had more inter-Haversian canals than 

 the outer, while the posterior ridge (linea aspera) had a much richer blood 

 supply than the anterior wall (pis. 28-35, figs. 372-453). 



In those femora which showed combinations of types, the proportions of the 

 units were found to vary greatly. In some the proportion of lamella? was 

 considerably over 50% of the whole bone, and in others varying percentages 

 of lamella? and lamina? from 50% to 0% were observed. In only a few cases the 

 femora composed of Haversian systems alone were without senile evidences. 

 From an examination of two entire human femora of the white race at intervals 



3 



