308 THE SOLIDS. 



ment of bone ; they are generally apparent in the third or 

 fourth tier of the. first formed and small cancelli, and while 

 the nuclei of the cartilage cells yet exist. (See Plate 

 XXXV. fig. 3.) 



It will now be perceived that the intra-cartilaginous form 

 of ossification is identical witk the intra-membranous type 

 in all essential particulars. 



It will also readily be seen, that this view of the process 

 of ossification differs very considerably from the more re 

 cently expressed opinions on the subject ; those, for example, 

 of Drs. Todd and Bowman, and of Mr. Tomes. 



The authors of the " Physiological Anatomy " consider that 

 the nuclei of the cartilage cells become developed ultimately 

 into the bone cells. 



There are many considerations which would lead to the 

 conclusion that such a transformation is but little probable, 

 the following of which may be referred to : 



The formation of bone independent of cartilage, as in the 

 intra-membranous type of ossification. 



The small number of the cartilage cells compared with the 

 vast quantities of bone cells which exist in even a young 

 bone. 



The impossibility of explaining why the permanent car- 

 tilages should not, like the temporary, be constantly sub- 

 ject to ossification, since they are both organised in precisely 

 the same manner. 



The proof that cartilage cells have no further stage of 

 development to pass through, manifested by the fact of the 

 occurrence of parent cells in all cartilages, whether temporary 

 or permanent. 



The chief new points contained in Mr. Tomes's views * are 

 the ossification of the walls of the several cartilage cells 

 which form each roll or column, and the conversion of a 

 number of these, by the absorption of the contiguous walls of 

 the cells, into a single cavity or tube, which becomes filled with 

 a granular blastema ; this tube Mr. T. considers to be an 



* See Art. Osseous Tissue, Cyclop, of Anatomy and Physiology. 



