CONNECTIVE TISSUES. an 
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 body 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, Pie, re, ie eeelaoe 
: . : : : tion of the skull ina three-day- 
into which the surrounding perichondrium  ¢id rabbit. bo, _ basioccipital 
: : : : bone; ch, occipital portion of 
extendssas an ossitication ridge. In-this — ‘ckoniroceanium: co, occipital 
region bone formation takes place, with ferdvi' £0) <xoccipital im 
the result that the whole structure is ° > 
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. 

