BONE 



{):^ 



canals. These are called \ Olkiiianirs canals and carry N'ascular 

 tissue into the Haversian canals. In many ])hices hiindles of 

 collagenous fibers from the ])eri()steum extend into the periosteal 

 l)one to form Sharper's fil)ers which tightly attach the periosteum 

 to the underh ing hone. 



Fig. 36. — Photograph of a longitudinal section of the developing rabbit femur. 

 Part of its diaphysis (below) and an epiphysis (above), show endochondral bone 

 formation. In both, the cartilage is resorbed and replaced by spongy bone, in 

 the epiphysis the final bone is irregular and spongy, but in the diaphysis Haversian 

 systems are formed. Growth of the intervening hyaline cartilage region and pro- 

 gressive resorption of it and replacement by bone make possible growth in length 

 of the bone. In the epiphysis there is a network of broad bony pieces and large 

 marrow cavities; in the diai^hysis there are more numerous thinner bony spicules 

 separated by narrow cavities. The majority of the bony strands here are deposited 

 paralleling the length of the bone along lines indicated by the paralleled columns of 

 cartilage cells which are resorbed as the marrow tissue extends. Fig. 35 shows the 

 right portion of the section in greater detail. 



Growth in thickness of a long bone is made possible liy resorption; 



this increases the central marrow cavity, and new bone is added 



as periosteal lamelht^. Resorption extends into ]M-imary Haversian 



systems, carrying along osteogenic tissue into the marrow ca\ities 



5 



