NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 29 



18. The presence of the early tlifferentiatious 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 lacunEP, and from their 

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

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

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

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



Reptiles. — The extension of lamellte and the further development of lamina; 

 and Haversian systems were seen in the femora of reptiles. 



Birds. — The extension of lamella3, prominent development of laminae, and 

 advancement of Haversian systems were observed in these animals. 



Mammals. — Extension of lamellfe, completion of lamina, and a much better 

 development of Haversian systems were observed in mammals. 



Man. — Extension of lamellae, laminae, and the completion of the Haversian 

 systems were seen in human femora. 



III. FETAL HUMAN FEMOEA 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 be 

 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 lacunje 

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

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

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

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

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

 were, the autero-posterior 1.8 mm., tlie lateral L5 mm., and of the canal 0.5 nun. 

 X 0.4 mm. (pi. 21, fig. 299). The antero-posterior diameter at tliis 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 tliose of tlic 

 medullary canal were 0.5 mm. X 0.5 mm. The canal was situated eccenti-ically 

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

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

 ing the twofold division (pi. 2], fig. 300). Comparing this section with tlie 



