Connective Tissues. 31 



its outstanding processes. In the shaft the formation of endochon- 

 dral bone is of short duration. Through the activity of the osteo- 

 blasts lying directly in the perichondrium, or later the periosteum, 

 a process of formation of intramembranous bone goes on during 

 the whole period of growth, and the result of the peripheral deposi- 

 tion of bone lamellae is, as described above, that the transverse 

 diameter of the bone is greatly increased. The enlargement of the 

 marrow cavity, with which this is associated, is produced by the 

 absorption of bone from the interior. 



In young animals both the epiphysial centres and the masses 

 of cartilage in which they are formed are sharply marked off from 

 the bod}' of the bone (cf. Fig. 13). This is largely because the 

 formation of the epiphysial centres tends to lag behind that of the 

 main centres, and thus the cartilage 

 extremities of the bones are evident long 

 after the formation of the shaft is under 

 way. In the epiphysial centres the bone 

 formation is endochondral. The bone 

 masses which they form are distinguished 

 as epiphyses. During the period of 

 growth they are connected with the body 

 of the bone by plates of epiphysial cartilage, fig. 12. The occipital por- 

 into which the surrounding perichondrium om" lbbft! k fo! n baSSftai 

 extends as an ossification ridge. In this %2&££^?c££S&& 

 region bone formation takes place, with ££££ mzJumT^w™- 

 the result that the whole structure is occi P ital - 

 greatly increased in length. 



After the period of growth, the duration of which differs in 

 different bones, the epiphyses become firmly co-ossified with the 

 body of the bone, although the lines of junction or epiphysial lines 

 may be still visible. Thus in the distal extremities of the radius 

 and ulna, in the proximal extremities of the fibula, or in the bodies 

 of the lumbar vertebrae, the epiphysial lines appear even in old 

 animals. In the foregoing figure (10) of the divided femur it will be 

 seen that the position of the epiphysial lines is indicated by bands 

 of compact tissue. Finally, in thoroughly macerated bones of 

 young animals, the epiphyses are usually found to be readily 

 separable from the bones. 



