116 Cc. V. MORRILL 
Distally the new formed epiphysis comes into relation with 
the embryonal cartilage which forms the new fibula and tibia 
(figs. 4 and 9) and later a joint appears at this level. As pre- 
viously stated, before the new epiphysis is completed and while 
a portion of the old epiphysis is still present (fig. 3) a close 
attachment is developed between the axial cartilage (Aw.C.) and 
the embryonal cartilage (Hm.C.). It is difficult to say whether 
or not the two cartilages become actually continuous. The 
tissue uniting them is composed of cells without definite bounda- 
ries and with small elongated nuclei. It does not appear to be 
cartilaginous. Small cavities soon appear in this connecting 
tissue, beginning usually at the circumference and spreading 
toward the interior. An early stage in the joint formation is 
shown in figure 9. The new joint cavity (J.c.n.) is just appearing 
between the new femoral epiphysis (Ep.f.n.) and the new fibula 
(Fib.n.). In a later stage (fig. 4) the joint cavity has enlarged 
at the circumference and a definite capsule has been formed, the 
latter being continuous with the perichondrium of the new 
cartilages (epiphyses). A small joint cavity has also developed 
between the fibula and a tarsal cartilage (7.c.n.). At this 
stage the fibula itself has begun to show evidences of subdivision 
into shaft and two epiphysis. In the central portion, the car- 
tilage areolae are enlarging and becoming more spherical pre- 
paratory to the formation of a marrow cavity, while at the sur- 
face a thin layer of subperiosteal bone has been laid down. In 
the epiphyseal portions, the cartilage cells have a tendency to 
arrange themselves in concentric ares, a characteristic of epi- 
physes in general. 
No attempt has been made in this study to arrange the speci- 
mens in a series based on time after operation. The stages of 
regeneration do not necessarily correspond to the intervals of 
time. For example figure 3 shows a stage obviously more ad- 
vanced than that shown in figure 2, yet it was taken from a 
specimen killed thirty-eight days after operation, while the latter 
came from one killed at forty days. This is very probably due 
partly to difference in time of healing of the wound and partly 
to temperature. It was noticed that among animals operated 
