DEVELOPMENT OF BONE. 129 



filled with medullary matter containing blood-vessels. These 

 spots, traversed by dilated canals, lend support to and confer 

 firmness upon the remains of the cartilage, which has now in 

 great part apparently undergone absorption, and is thoroughly 

 impregnated with granular deposits of lime. In the neigh- 

 bourhood of these spots the cartilage appears transparent and 

 composed of large clear cells separated from one another by 

 only a small portion of matrix. When a more careful exami- 

 nation is instituted, it is observable, however, that the limits 

 of the cavities filled with medulla, and the large-celled car- 

 tilage region, on the one hand, and the limits of the calcified 

 trabeculae and the large-celled cartilage region on the other, 

 do not coincide ; for the calcified portion may be followed 

 beyond the limits of the medullary spaces, and terminates 

 in the form of fine processes in the larger trabeculse of the 

 matrix of the still unpenetrated cartilage. The cells at the 

 limits of the latter appear to occupy the tubular extremities 

 of the calcified tissue, and there first come into contact with 

 the medulla. Such are the processes in cartilage that precede 

 the formation of bone. Osseous tissue is only developed in 

 those parts where medullary substance has been first formed, 

 and, indeed, upon its surface, being superimposed upon the 

 previously calcified cartilage. In regard to this point, how- 

 ever, a fuller description will hereafter be given. It is not 

 difficult to see these phenomena in the centres of ossification 

 of the short bones, or in the diaphyses of the long bones. The 

 centres of ossifications of the epiphyses which appear at a later 

 period are also exceedingly well adapted for observations of 

 this kind. The embryoes from which the preparations are 

 made ought previously to be macerated in chromic acid, or still 

 better, in Miiller's fluid. The most instructive specimens are 

 furnished by keeping the preparations for a somewhat longer 

 time in the latter fluid till they can be cut with facility, and 

 then staining them with carmine. 



The changes described gradually extend from the centre of 

 ossification into the adjoining cartilage. Longitudinal sections 

 through the diaphyses of foetal bones, which display the 

 margins undergoing ossification, are best adapted for microscopic 

 investigation. The appearances presented by such a longitu- 



