256 



COMPARATIVE ANATOMY 



The shafts of the radius and ulna begin to ossify about the middle of 

 the second month. The bony epiphysis of the olecranon process appears 

 at ten years and unites with the shaft at sixteen years. The epiphyses of 

 the radius appear earlier and fuse with the diaphysis later. (Fig. 211) 



The wrist bones are cartilaginous at birth but begin to ossify during 

 the first year, the pisiform last of all during the tenth to twelfth years. 

 Metacarpals and phalanges ossify relatively early, beginning with the 

 third month. Diaphysis and epiphyses are formed as in all long bones. 



VESSELS 



UOWER END AT BIRTH 



Fig. 213. — Diagrams illustrating the development of the thigh-bone from birth to 

 the twenty-fifth year. Since the marrow cavity of the adult bone is large enough to 

 contain the entire bone of the new-born infant, it is obvious that the growth of the bone 

 involves continuous destruction of the bone from within as well as additions to the 

 outside. (Redrawn after Keith.) 



Development of the Lower Limb. The concentration of connective 

 tissue to form the anlage of the pubis and femur begins in the fifth week 

 of fetal life. At the time when cartilage first appears, the axis of the coxal 

 bone, which primarily stood at right angles to the vertebral column, shifts 

 backward and comes to lie parallel with the backbone. Connexion with 

 the sacrum begins with the sixth week. By the end of the second month, 

 all of the elements of the pelvic appendage including the coxal are per- 

 formed in cartilage. Ossification of the shaft of the femur usually occurs 

 bv the end of the second month. 



