66 



THE CONNECTIVE TISSUES. 



[CH. v. 



long bone consists and 

 the adult bone there 

 are several intermediate 



Fig. 89. Section of two foetal phalanges ; the car- 

 tilage-cells in the centre of B are enlarged and 

 separated from one another by calcified matrix. 

 im, layer of bone deposited under the perios- 

 teum, o, layer of osteoblasts by which this 

 layer was formed. The rows of cartilage-cells 

 are seen on each side of the centre of calcifica- 

 tion. In A, the terminal phalanx, the changes 

 begin at the tip. (After Dixey.) 



The process may, how- 

 ever, be most conveniently 

 described as occurring in 

 three principal stages. 



The first stage consists 

 of two sets of changes, one 

 in the cartilage, the other 

 under the perichondrium. 

 These take place side by 

 side. In the cartilage the 

 cells in the middle* be- 

 come enlarged and separated 

 from one another. The car- 

 tilage-cells on each side get 

 arranged in rows in the 

 direction of the extremities 

 of the cartilaginous rod. 

 If at this stage one cuts 

 the little embryonic bone 

 with a knife, the knife en- 

 counters resistance, and 

 there is a sensation of 

 grittiness. This is due to 

 the fact that calcareous 

 particles are deposited in 

 the matrix ; and in conse- 

 quence of this the matrix 

 stains differently with his- 

 tological reagents from the 

 unaltered matrix. Simul- 

 taneously with this, the 

 periosteal tissue is forming 

 layer after layer of true 

 bone ; this is formed exactly 

 in the same way as in 



* This is the case in nearly 

 all the long bones, but in the 

 terminal phalanges the change 

 occurs first, not in the middle 

 but at their distal extremities. 



