CONNECTIVE TISSUES 47 



actively, and, instead of forming new cartilage, eat away the 

 material, and thus open out spaces (fig. 14, 6). Into these 

 spaces processes of the perichondrium bore their way, carry- 

 ing with them blood-vessels, and thus rendering the cartilage 

 vascular. The vascularisation of the centre of the cartilao-e 

 having been effected, the process of absorption extends 

 towards the two ends of the shaft of cartilage, which con- 

 tinues to elongate. The cartilage cells divide and again 

 divide, and, by absorbing tlie material between them, form 





"^^Ji^&r.'jLi'-^ 





M 



S' 



- / 



.i§:.'y>^im§ik 







Fig. 14. — Intra-cartilaginous Bone Development. A phalanx of a fretal 

 finger showing the formation of periosteal bone round the shaft (a) ; 

 the opening up of the cartilage at the centre of ossification and the 

 vascularisation of the cartilage by the invasion of fibrous tissue (b) ; 

 and the calcification of the cartilage round the spaces (c). 



long irregular canals running in the long axis of the bone, 

 with trabeculse of cartilage between them. Into these 

 canals the processes of the periosteum extend, and fill them 

 with its fibrous tissue. A deposition of lime salts takes 

 place upon the trabeculse, enclosing cells of the invadino- 

 fibrous tissue, and thus forming a crust of bone, while the 

 cartilage also becomes calcified. If this calcification of the 

 cartilage and deposition of bone were to go on unchecked, 

 the block of cartilage would soon be converted to a solid 

 mass of calcified tissue. But this does not occur. For, as 

 rapidly as the trabeculse become calcified, they are absorbed, 



