CH. V. 



DEVELOPMENT OF BONE. 



of the shaft. Here the osteoclasts have again to do the work, 

 and, with this final act of destruction, all remains of any calcified 

 cartilage of the foetal bone entirely disappear. 



The formation of a so-called cartilage bone is thus, after all, a 

 formation of bone by subperiosteal 



tissue, just as it is in the so-called *p s <= " ^ M I g 

 membrane bone. S 2" S: j= ^ ^ ^ 



After a time the cartilage at the 

 ends of the shaft begins to ossify 

 independently, and the epiphyses 

 are formed. They are not joined 

 on to the shaft till late in life, so 

 that growth of the bone in length 

 can continue till union takes place. 



Bone grows in width by the 

 deposition of layers under the perios- 

 teum, like successive rings formed 

 under the bark of a growing tree. 

 This was shown long before the 

 histological details which we have 

 described were made out by Sharpey. 

 Silver rings were placed by Duha- 

 mel around the bones of young 

 pigeons. When killed later, the 

 rings were completely covered in by 

 bone ; and in the animals killed 

 last, were even found in the central 

 cavity. Another series of experi- 

 ments with pigs was made by the 

 celebrated John Hunter. The young 

 animals were fed alternately on 

 ordinary food and food dyed by the 

 red pigment madder. The new bony 

 tissue acts like what dyers called a "mordant " : it fixes the dye, 

 and the rings of bone deposited during the madder periods were 

 distinctly red in colour. 



The importance of the periosteum in bone formation is now 

 recognised by surgeons. When removing a piece of bone they 

 are careful, if possible, to leave the periosteum behind : this leads 

 to regeneration of the lost bone. If it is absolutely necessary to 

 remove the periosteum, successful cases have occurred in which 

 the living periosteum from an animal has effectively been 

 transplanted. 



Fig. 91. Longitudinal section of ossi- 

 fying cartilage. Calcified trabeculae 

 are seen extending between the 

 columns of cartilage-cells. . car- 

 tilage-cells ; a, b, secondary areolw. 

 x 140. (Sharpey.) 



