NO. 3 



COMPARATIVE HISTOLOGY OF FEMUR FOOTE 



149 



XI. MAN 



One hundred and thirty-nine femora were examined. 



General Character of the Femur 

 The femur of man presents a variety of shapes.- 



The medullary canals are generally full of cancellous hone, the meshes of 

 which are rilled with marrow. The medullary surfaces are almost always 

 rough, but in some round sections the surfaces are smooth and cancellous 

 bone is absent. 



The average medullary index of the adult is 38.6%. Comparing the aver- 

 age index of man with that of other mammals, which is 63.3%, it will be noticed 

 that the medullary canal is proportionately smaller and the wall of the bone 

 thicker in man than in other mammals, or in bipeds than in quadrupeds. 



The following types and combinations of types are found: the third, first 

 and third, second and third, and first, second, and third. The third type occurs 

 in the (la), (lb), and (C) forms of differentiation. The pure third type bone 

 without senile changes is rather infrequent. The human series consists of the 

 fetal, infantile, adolescent, and adult femora. The fetal series includes the 

 white and black races ; the infantile, the yellow-brown, ancient Egyptian, and 

 modern white races; the adolescent, the yellow-brown, ancient Egyptian, and 

 white races ; and the adult, all races. 



Fetal Human Femora 

 Seven femora were examined. 



In the very young fetus of two to three months, basic bone substance is 

 present and is marked off into regular areas by crude, branching canals. As 

 fetal life advances the canals become less branching and more concentric. Grad- 

 ually the basic bone becomes lamellated and then develops into the second type 

 and remains so until birth. Throughout childhood and youth the lamina? tend 

 to disappear and to be replaced by Haversian systems, until the bone develop- 

 ment is completed. 



In the formation of human fetal femora the following plan was observed. 

 A horseshoe-shaped band of lamella? or lamina 1 with oval lacunas and bushy 

 canaliculi is formed around the medullary canal, with the exception of the pos- 

 terior ridge which appears to have an independent formation at a later date. 

 As the bone develops the ridge fuses with the lateral wall. 



RIGHT FEMUR OF A WHITE FETUS, TWO AND ONE-HALF MONTHS OLD 



Pl. 21. Fig. 29!). Six. Tab. VIII 

 Antero-posterior diameter of bone, 1.8. ; lateral, 1.5 mm. 

 Antero-posterior diameter of medullary canal, 0.5 mm.; lateral, 0.4 mm. 

 The medullary canal is full. Medullary index, 8%. 



