OSSIFICATION OF CARTILAGE. 169 



in the substance of the latter, which are preparatory to its conversion into 

 Bone. Instead of single isolated cells, or groups of two, three, or four, such 

 as we have seen to be characteristic of ordinary Cartilage (Fig. 52), we find, 

 as we approach the centre or line of ossification, clusters made up of a larger 

 number arranged in a linear manner; which seem to be formed by a continu- 

 ance of the same multiplying process as that formerly described (Fig. 66). 

 And when we pass still nearer, we see that these clusters are composed of a 

 yet greater number of cells, which are arranged in long rows, whose direc- 

 tion corresponds to the longitudinal axis of the bone ; these clusters are still 

 separated by intercellular substance ; and it is in this, that the ossific matter 

 is first deposited. If we separate the cartilaginous and the osseous substance 

 at this stage of the process, we find that the ends of the rows of cartilage- 

 cells are received into deep narrow cups of bone, formed by the calcification 

 of the intercellular substance between them. Thus the Bone first formed in 

 the cartilaginous matrix, is seen to consist of a series of lamellae of a some- 

 what cylindrical form ; inclosing oblong areolse, or short tubular cavities, 

 within which the piles of cartilage-cells yet lie : and it thus corresponds 

 closely with the reticular structure, which first makes its appearance in the 

 intra-membranous form of the process. So far it would appear that the blood- 

 vessels are not directly concerned in the operation; for although they advance 

 to the near neighbourhood of the first ossific deposit, they do not make their 

 way into its substance, or even into the intervening areolte. 



199. This state of things, however, speedily gives place to another. On 

 examining the subjacent portion, in which the ossification has advanced further, 

 it is found that the original closed cavities have coalesced to a certain extent 

 (probably by the absorption of their walls), both laterally and longitudinally; 

 and that they now receive numerous blood-vessels, prolonged into them from 

 the previously-ossified portion. The groups of cartilage-cells, which origi- 

 nally occupied the cavities, are no longer seen ; and their place is filled with 

 a blastema, composed of cells, containing a granular matter, and closely re- 

 sembling those seen in the intra-membranous ossification, with a few fibres 

 scattered amongst them. It is by a change in this blastema, that the walls of 

 the cavities are gradually consolidated; new deposits of ossific matter being 

 formed in their interior, which occasion the gradual contraction of the cavities, 

 and give an increasing density to the bone. The cancellated structure, which 

 remains for a time in the interior of the long bones, and which continues to 

 occupy their extremities, represents the early condition of the ossifying sub- 

 stance, with very little change ; whilst the cavities, which have formed more 

 regular communications with each other, and which have been gradually con- 

 tracted by the subsequent deposit of concentric lamella?, one within another, 

 form the original Haversian canals. Thus we see that they all form one 

 system in their origin ; as they may be considered to do, notwithstanding 

 the difference of their form, in the complete bone. 



200. The original osseous lamella?, formed by the consolidation of the car- 

 tilaginous substance, are entirely composed of granular matter ; and exhibit 

 none of the lacunae and canaliculi, which are commonly regarded as charac- 

 teristic of Bone. These excavations present themselves, however, in all the 

 subsequent deposits ; and into the origin of these, we have now to inquire. 

 According to the views of some Microscopists, the cells of the blastema fill 

 themselves with ossific. matter, except at the points occupied by the nuclei ; 

 at the same time, they become flattened against the walls of the canals, and 

 their nuclei send out radiating prolongations ; so that, when the calcification 

 of the cell has been completed, a stellate cavity is left in the hard deposit, 

 which is occupied by the granular matter of the nucleus. The centre of this 

 cavity forms the lacuna, in which the original granular matter may frequently 



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