DEVELOPMENT OF BONE. 



137 



Fig. 14. 



In such cases the cartilage, either in a pure state, or per- 

 forated by canals, and calcified, and in the preparatory stage 

 of intra-cartilaginous ossification, becomes enclosed in a tube of 

 osseous tissue * In certain animals, medullary substance re- 

 places cartilage in the middle portion of the bone; whilst in 

 other animals, and also towards the apophyses of the bones in 

 the former instances, a few intra-cartilaginous bony trabeculse 

 are developed, which become altered to the 

 periosteal tube. In a few cases, as for ex- 

 ample in sections of the tubular bones of the 

 extremities of the adult Proteus, we find an 

 osseous tube composed of a few periosteal 

 lamellae, the cavity of which is filled with true 

 cartilage that has undergone calcification. 



An easily intelligible diagram, showing intra- 

 cartilaginous and periosteal ossification proceed- 

 ing together, as occurs in the formation of the 

 long bones of the higher vertebrata,is exhibited 

 in the adjoining figure (fig. 14), by H. Meyer ;f 

 a b c indicate the bone of an infant ; A b c 

 the form which the bone of the adult acquires 

 by intra-cartilaginous growth, whilst its in- 

 crease in breadth results from the periosteal 

 deposit p. The ossific capacity of the peri- 

 osteum causes a reproduction of bone to occur 

 if the latter be resected from its investing 

 periosteum.^ Upon this circumstance depend 

 the osteo-plastic processes that have been ob- 

 served after the transplantation of excised por- 

 tions of periosteum, and which are especially active in young 

 animals, and to some, though a smaller extent in adults . The 

 peculiar histological processes occurring in periosteal ossifica- 

 tion have been fully discussed by Virchow, and more recently 



* Duges, Rathke, Bruch, Reichert, H. Miiller, loc. cit., p. 193. 

 t Miiller's Archiv, 1849, p. 292. 



J Heine, Grafe and Walther's Journal, 1839, p. 513, and many recent 

 observers. 



Oilier, Journal de la Physiologic, Tom. ii., pp. 1 and 169. 



