280 Studies of the Development of the Hainan Skeleton 



section throngh the leg of Embryo CLXXV, length IS mm. The de- 

 velopment is slightly more advanced than in Embryo CIX. 



The further general development of the skeleton of the limb may be 

 followed in Figs. 8 to 13. For the sake of convenience the development 

 of the several parts of the skeleton will be taken up in turn as follows: 

 (a) pelvis; (b) femur, hip-joint, tibia and fibula, and knee-joint; (c) 

 ankle and foot. 



A. PELVIS. 



Petersen, 93, has given a good account of the early development of the 

 human pelvis. His Avork was based upon embryos belonging to the His 

 collection. In embryos Eu, length 9.1 mm., Ko, length 10.2 m.m., and 

 IST, length 9.1 mm., the formation of the lumbo-sacral plexus has begun 

 and there is a condensation at the center of the limb-bud. The conditions 

 here resemble those in Embryo CLXIII, length 9 mm., Fig. 2, described 

 above. Petersen believed that the condensation of tissue in embryos Eu 

 and Ko represents the germinal area for the muscles and skeleton of the 

 lower extremity while that of IST shows a further differentiation of the 

 diaphysis of the femur. The last ends anteriorly in a small undifferen- 

 tiated cell-mass but there is nothing further to indicate the future pelvis. 

 Yet, as I have mentioned above, the relations of this cell-mass to the 

 nerves arising from the plexus indicates that it is the fundament of the 

 future pelvis. The nerves pass about it as they do later about the ace- 

 tabulum. In Embryo S^, length 12.6 mm., Petersen found what he con- 

 siders the first traces of a definite pelvic fundament. This embryo is 

 evidently of about the same stage of development as CIX, length 11 mm.. 

 Figs. 3 and 4 and 46 to 53. But CIX is slightly more advanced and 

 shows early stages of chondrofication not seen in S^. The pelvis of S^ 

 has a slightly more anterior position and the iliac blastema extends rather 

 toward the 24th than the 25th vertebra (Fig. 1, Plate I, of Petersen's 

 article) . 



The pelvic scleroblastema of embryos of the stage found in CIX 

 undergoes a rapid development. Its iliac portion extends in a dorsal 

 direction toward the vertebrae which are to give it support. The costal 

 processes of the latter at the same time become fused into an auricular 

 plate. With this the iliac scleroblastema comes into close approxima- 

 tion. Figs. 5 and 6, Plate III, although for some time separated by a 

 narrow band of tissue staining less densely than the blastemal. Fig. 37. 



Anteriorly the iliac blastema extends toward the abdominal muscula- 

 ture, to which it finally serves to give attachment. 



While the blastemal ilium is thus becoming differentiated the pubic 



