Charles E. Bardeen 393 



In Embryo CXLV, length 33 mm., Figs. 11 and 12, the process of 

 cartilage formation has given rise to structures which resemble adult 

 bones. The tibia has greatly expanded at its distal extremity and now 

 articulates. directly with the fibula. These two bones in turn articulate 

 with the well-developed superior articular process of the astragalus. The 

 malleolar process of the tibia is larger and extends further distal than that 

 of the fibula. In an embryo of a corresponding age, however, Schomburg 

 shows that the fibula extends further distal than the tibia. Individual 

 variation may exist. 



The astragalus exhibits perhaps more marked alterations in form than 

 any other bone of the foot during the period when the embryo is growing 

 from 20 to 30 mm. in length. Toward the tibia and fibula it develops 

 a well-marked articular process. While this resembles closely the similar 

 process in the adult it is less developed on its fibular side than it is in 

 the adult. As Schomburg has shown the definite adult form is not 

 reached before the fourth month. Toward the calcaneus the bone is 

 well developed and against it exhibits the two characteristic articular 

 surfaces. The posterior of these, compared with the adult, is relatively 

 undeveloped. Distally the bone sends forth a rounded process to articu- 

 late with the navicular. In the material at my disposal the whole com- 

 plex astragalus seems to arise from a single primary center. 



The calcaneus, like the astragalus, undergoes marked changes in form 

 during the latter part of the second and the first part of the third month 

 of development. Toward the heel a well-marked tuberosity has made its 

 appearance in Embryo CXLV, Figs. 11 and 12. Distally the bone ex- 

 tends to form a joint with the cuboid. Tibially it has developed a 

 sustentaculum tali for articulation with the astragalus. It is still, how- 

 ever, short in proportion to its width as compared to the adult. 



The navicular exhibits no marked changes. On its plantar side and 

 tibial edge it shows a distinct tuberosity. 



The cuneiform bones are crowded together and have their character- 

 istic wedge shape. The internal cuneiform is the largest and extends 

 farthest distal. The middle is the smallest. 



The cuboid shows a tuberosity. The phalanges, all of which are de- 

 veloped, present no points of special interest. 



The joint-cavities begin to develop while the embryo is growing from 

 25 to 30 mm. in length. As in other cases, so here the blastemal tissue 

 in which the cartilages are developed becomes condensed at their articu- 

 lating ends and about the joint, while in the region of the joint the tissue 

 becomes less dense and finally disappears leaving a joint-cavity. In 



