DYNAMICS OF HISTOGENESIS 



99 



ture is an opposing factor to be considered as extrinsic pressures 

 limiting the relative volume of the femur to the thigh. 



With the rapid increase of limb weight and with increase of 

 opposition to growth at the ends of the femur, together with the 

 resistances manifested by muscular reaction, the density of the 

 femur progressively increases (tables 2 and 3 and chart B). 



TABLE 1 



This increase in density is going on simultaneously with the 

 relative decrease in femoral volume as the growth of the limb 

 advances. In an 18-mm. embryo, the volume of the femur con- 

 stitutes one-fifth that of the entire limb, whereas its density is 

 1.025. In a 38-mm. embryo, femoral volume is one-sixth that 

 of the limb and its density is 1.055; whereas, in the 50-mm. 

 embryo, the volume of the femur is one-seventh and the density 

 1.075. The density of the femur in a 20-cm. embryo is 1.6 and 

 the volume is one-sixteenth that of the limb. (Chart B.) 



