288 Studies of the Development of the Human Skeleton , 



muscle tendons and fascia are inserted. But in embryos up to 50 mm. 

 in length there is no extension of cartilage into this area. Since by this 

 period the shaft is ossified it is evident that no cartilagenous linea aspera 

 is formed. 



Ossification begins at an early period kneewards from the center of the 

 shaft. Endochondral calcification begins here in embryos about, or 

 slightly less than 20 mm. in length. Perichondral ossification usually 

 begins in embryos about 25 mm. long, although in Embryos LXXXVI 

 and LXXV, length SO mm., the clavicle alone shows actual bone forma- 

 tion. Ossification of the femur takes place at about the same time as 

 that of the humerus, radius and ulna, and very slightly, if at all, precedes 

 that of the tibia. Ossification of the clavicle and the superior and in- 

 ferior maxillary bones seems always to begin a little earlier, that of the 

 scapula, ilium, occipital, and ribs, slightly later. 



The distal extremity of the femur is large at an early period of differ- 

 entiation, Embryo CIX, Figs. 3 and 4. In Embryo CXLIV, length 

 IJlf mm.. Figs. 5 and 6, it has expanded laterally and each lateral process 

 has extended dorsally so that fairly well-marked condyles are apparent. 

 These are better formed in Embryo XXII, length 20 mm.. Figs. 9 and 

 10. In CXLV, length 33 mm., Figs. 11 and 12, the form of the distal 

 extremity of the femur resembles the adult. 



The tibia and fibula at first lie nearly in the same plane. Embryo CIX, 

 length 11 mm.. Figs. 3 and 4. As the head of the tibia enlarges toward 

 the knee-joint it comes to lie dorsal to the proximal extremity of the 

 fibula. This may be seen in Embryo CXLIV, Figs. 5 and 6, and more 

 marked in Embryo XVII, length 18 mm.. Fig. 59; XXII, length 

 20 mm.. Figs. 9 and 10; and CXLV, length 33 mm.. Figs. 11 and 12. 

 In the last embryo the relations of the head of the fibula to that of the 

 tibia are nearly like the adult. 



In Embryo CIX, Figs. 3 and 4, the fibula points toward the lateral 

 condyle of the femur and the tibia toward the median, but the long axis 

 of the femur much more nearly meets that of the tibia than that of the 

 fibula. As the head of the tibia enlarges the anterior extremity of the 

 long axis of the bone is carried toward the center of the distal end of the 

 femur while the head of the fibula is pushed toward the side, Figs. 5, 6, 

 59, 9, 10, so that the long axis of the fibula comes to point lateral to 

 the extremity of the femur. The head of the fibula is held in place by 

 ligaments developed from the skeletal blastema. 



The development of the knee-joint in man has been studied by a 

 number of competent observers. Bernays, in 1878, gave a good review 

 of the previous work of von Baer, Bruch, Henke and Eeyher, and an 



