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- 



FIG. 43. 



Enlarged view of a portion of a section through the phalanx of a mammalian foetus showin; 

 the development of bone (from a preparation lent by Dr. G. Mann). 1, hyaline cartilage matrix 

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

 fied cartilage matrix ; 6, blood-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 



