6 4 



CARTILAGE AND BONE 



first supposed. In ontogeny it is the latest to appear ; it is formed 

 chiefly in the region of the epiphyses, and is almost entirely of a 

 purely provisional character. By far the greatest bulk of the endo- 



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3-— t^J%,^ ^^^ 



sG> <£* *■* <" ^ ^ 



<g> <s> 







Fig. 43. 



Enlarged view ofa portion ofa section through the phalanx of a mammalian foetus showing 



the developmenl of I (from a preparation lent by Dr. G. Mann). 1, hyaline cartilage matrix ; 



•j, cartilage cell ; 3 and 4, the same becoming modified near the region of ossification ; 5, calci- 

 fied cartilage matrix ; 6, bl l-vessels invading the cartilage ; 7, osteoblasts depositing bone ; 



8 island of cartilage, remains of matrix surrounded by newly-deposited bone : 9, endochondral 

 bone substituted for cartilage; 10, perichondral bone deposited outside; 11, bone-cell; 12, 

 invading cells destroying cartilage. 



skeleton is of the second or sub-pcriosteal variety. This is the first 

 bone to appear in the ossification of the limb-bones, for instance, 

 and is deposited layer upon layer by the osteoblasts lining the 



