28G Studies of the Development of the Iluiuaii Skeleton 



pelvis and refers to the previous literature on that subject. He shows 

 that the sacrum and the innominate bones exhibit a certain independence 

 in rate of growth. 



B. FEMUR AND HIP-JOINT, TIBIA, FIBULA, AND KNEE-JOINT. 



The rapid development of the blastemal skeleton of the lower limb has 

 been briefly described above. Soon after the fundament of the femur 

 makes its appearance condensation of tissue marks out the anlage of the 

 tibia and fibula and the skeleton of the foot. This last seems to be at 

 first a somewhat irregular continuous sheet of tissue. It is not clear 

 whether or not the anlage of the tibia and fibula also begins as a con- 

 tinuous tissue sheet which becomes divided, bv' ingrowth of blood-vessels, 

 into tibial and fibular portions. The incomplete development of the 

 interosseous fissure in Embryo CIX, Icngtli 11 mm., Figs. 3 and 4, sug- 

 gests this. The blastemal anlages of the tibia and fibula are here very 

 incompletely separated. 



In Embryo CIX the femoral blastema is continuous at one end with 

 that of the pelvis, at the other with that of the tibia and fibula and that 

 of the last two with the foot-plate. 



Within the blastema of the femur, tibia and fibula chondrofication 

 begins as soon as the outlines of the blastemal skeleton are fairly com- 

 plete (Figs. 3 and -i). The embryonic cartilage appears slightly knee- 

 wards from the center of the shaft of each bone and then extends toward 

 the ends. In CIX, Figs. 3 and 4, and 46 to 53, the cartilage of the 

 femur consists of a bar largest at the knee whence it tapers off toward 

 the hip. The cartilages of the lower leg lie nearly in a common plane. 

 That of the tibia is larger than that of the fibula and toward the knee 

 it broadens out considerably. At this stage the joints consist of a solid 

 mass of mesenchyme, Fig. 55. The tissue imiting the femur and tibia 

 has something the appearance of precartilage. 



The further development of the thigh and leg may be conveniently 

 studied by taking up at first the development of the femur and hip-joint, 

 and then that of the tibia, fibula and knee-joint. 



The cartilagenous femur expands rapidly at the expense of the sur- 

 rounding blastemal perichondrium and at the same time acquires adult 

 characteristics. 



In an embryo of 11^ mm., CXLIV, Figs.' 5 and G, the shaft of the femur 

 extends almost directly into the hip- joint. Here there is a simple rounded 

 head, distal and dorsal to which a slight projection marks the beginning 

 of the great trochanter. There is nothing corresponding to a true 



