NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 29 



18. The presence of the early differentiations of type in some black, 

 yellow-brown, white, and Egyptian femora, and of the late or complete dif- 

 ferentiations in other femora of the same races was observed. 



The following evidences of type advancement appear in the different classes 

 of animals : 



Amphibians. — A change of round to oval and long lacuna?, and from their 

 diffuse to their concentric arrangements, a transformation of basic to lamellated 

 bone, the separation of the uniformly lamellated bone structure into a twofold 

 or threefold division, and the formation of distinct lamina 1 and Haversian 

 canals in the walls of the femora, were all observed in the amphibians. 



Reptiles. — The extension of lamellae and the further development of laminae 

 and Haversian systems were seen in the femora of reptiles. 



Birds. — The extension of lamella 1 , prominent development of lamina 3 , and 

 advancement of Haversian systems were observed in these animals. 



Mammals. — Extension of lamella?, completion of laminae, and a much better 

 development of Haversian systems were observed in mammals. 



Man. — Extension of lamellae, lamina?, and the completion of the Haversian 

 systems were seen in human femora. 



III. FETAL HUMAN FEMORA AND THEIR FURTHER DEVELOPMENT 



Type differentiations, changes in the medullary index, and position of the 

 medullary canal, development of the linea aspera, and changes in the shape of 

 the shaft of the femur, are shown very interestingly in these bones, as may he 

 seen from the following descriptive observations. 



The fetal bones examined, mostly of the white race, varied in age from two 

 and one-half to nine months. The young bones of two and a half months 

 were composed of a crude, undifferentiated bone substance, with round lacuna? 

 and short, bushy eanaliculi, enclosing large irregularly shaped meshes. The 

 medullary canal was very small and irregular in shape, and together with the 

 meshes was filled with marrow. It was situated in the center of the section, and 

 immediately surrounded by a narrow ring of lamellae, thus showing the twofold 

 division observed in some of the lower animals. The diameters of the bone 

 were, the antero-posterior 1.8 mm., the lateral 1.5 mm., and of the canal 0.5 mm. 

 X 0.4 mm. (pi. 21, fig. 299). The antero-posterior diameter at this stage of life 

 was longer than the lateral. A little later (three to three and one-half months) 

 the same diameters were respectively 2.5 mm. X 2 mm., while those of the 

 medullary canal were 0.5 mm. X 0.5 mm. The canal was situated eccentrically 

 in the anterior half of the section, was only a trifle larger than the canal of 

 the younger bone, and was surrounded by a narrow ring of lamella?, also show- 

 ing the twofold division (pi. 21, fig. 300). Comparing this section with the 



