290 



HISTOGENESIS 



Cfl; tilaga. 



-Bone paraphysis 



-Bone : 



resorbed centrally to form large marrow spaces. Eventually, all of the cartilage 

 matrix, and probably the cartilage cells as well, are destroyed. 



Perichondral Ossification. — Compact bone is developed after birth by the 

 osteogenic layer of the periosteum and thus are produced the periosteal lamellcB. 

 In the ribs this is said to be the only method of ossification. The bone lamellas 

 deposited about a blood vessel are concentrically arranged and form the concentric 

 lamellcB of a Haversian system. The Haversian canal of adult bone is merely the 

 space occupied by a blood vessel. 



Growth of Cartilage Bones. — In cartilage bones there is no interstitial growth 

 as in cartilage. Most of the cartilage bones have more than one center of ossi- 

 fication and growth is due to 

 Cartilage ^^^ expansion of the interven- 



ing cartilage. Flat bones grow 

 at the periphery; ring Hke 

 bones, such as the vertebras, 

 have three primary centers 

 of ossification, between which 

 the cartilage continues to grow 

 (Fig. 296 A). In the case of 

 the numerous long bones of 

 the skeleton, the primitive ossi- 

 fication center forms the shaft 

 or diaphysis (Fig. 296 C-F). 

 The cartilage at either end of 

 the diaphysis grows rapidly 

 and thus the bone increases 

 in length. Eventually, osteo- 

 genic tissue invades these car- 

 tilages and new ossification 

 centers, the epiphyses, are formed, one at either end. When the growth of the 

 bone in length is completed, the epiphyses, by the ossification of the intervening 

 cartilage, are united to the diaphysis. 



The shaft of the long bones grows in diameter by the peripheral deposition 

 of bone lamellae and the central resorption of the bone. In the larger long bones 

 spongy, or cancellated, bone tissue persists at the ends, but in the middle portion 

 a large medullary, or marrow cavity, is developed. This is filled chiefly with fat 

 cells and constitutes the yellow lone marrow. 



Epiphysis 



Paraphysis 



Epiyhysis 



Fig. 296.— Diagrams to show the method of growth of 

 A, a vertebra; B, of sacrum; C-F, of a long bone (the 

 tibia). 



