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t THE CONNECTIVE TISSUES. *u4^cU**^5 B O- 



^^ ^ xvT^txWv/. >n^W-' . 



meshes of the tissue contain great numbers of soft, plastic connective- 

 tissue elements, the marrow-cells, which, while closely resembling 

 the leucocytes, differ from the blood-cells in possessing a nucleus larger 

 but less rich in chrqmatin. Larger eosinophilic cells, modifications 

 of the marrow-cells, are also encountered. Additional huge multinu- 

 cleated elements exist as the giant-cells, or myeloplaxes (Robin) ; 

 these are of interest as being especially concerned in the absorption 

 of osseous tissue, being identical with the osteoclasts (Kolliker). 

 Developing nucleated red blood-cells the erythroblasts are im- 

 portant constant elements. Mast-cells, with eosinophilic granules, 

 are also found as occasional constituents of the red marrow. 



Dentine is analogous to bone, although differing in details of 

 arrangement, since it is derived from embryonal connective tissue. 

 The matrix becomes calcified, and contains, embedded within the 

 ground-substance, numerous long, parallel, partly-branched tubes, 

 the dentinal tubules. These correspond with the lacunae of bone, 

 enclosingtn ~some places delicate processes, the dentinal fibres. 

 A more extended account of the structure and development of den- 

 tine will be found in connection with the structure of the teeth. 



Development of Bone. With the exception of the bones of 

 the vault of the cranium, of the face, and of part of the lower jaw, 

 the skeleton is mapped out, in its fcetal condition, by solid cartilages 

 which correspond in form more or less 

 closely with the future bones. The FIG. 59. 



primary embryonal cartilage is of 

 the hyaline variety, being extremely 

 rich in cells, many of which are engaged 

 in division; the cell-groups are separated 

 by a relatively small amount of inter- 

 cellular substance, and the outer surface 

 of these solid cartilages is closely in- 

 vested by an important membrane, the 

 primary periosteum. 



When bone is formed at the Centres Primary embryonal cartilage repre- 



r ( , . i i M senting one of the carpal bones : p, 



Of OSSlficatlOn Within the Cartilage, It IS per i c hondrium, or primary periosteum; 



termed CndOChondral bone ; when * nutr 'ent canals extending from the 



formed directly from and beneath the periphery - 

 periosteum, periosteal bone. While quite complicated in its 

 sequence of changes, it must be remembered that endochondral 

 development results in the formation of structures which are largely 

 temporary, and which finally, for the most part, suffer absorption. 

 The permanent bones of the skeleton are, chiefly, the products of 





