320 SPECIAL HISTOLOGY. 



There is another point in the development of the bone-cells still ob- 

 scure, or at least that has not been directly observed, viz., how their 

 pores or canaliculi become branched cavities, communicate with those of 

 other cells and acquire open orifices in certain situations. All that is 

 apparent in rachitic bone and elsewhere, is merely the circumstance, 

 that the thickening of the ossifying cartilage-cells does not proceed with 

 a straight but with an indented border, which is the case in fact from 

 the beginning up to their completion, and that the bone-cells have, at 

 first, more simple prolongations than afterwards. Observation teaches 

 nothing beyond this. Now, as there can be no doubt that the canaliculi 

 anastomose very freely, and also, that they frequently open on the outer 

 surface of the bone, or into the cavities in its interior, I do not for a 

 moment hesitate to express the opinion, that the canaliculi, arising as 

 simple branches from the lacunce, are continued or further developed by 

 absorption of the already -formed bone-substance. How such an absorp- 

 tion takes place, cannot, it must be confessed, be explained ; but that 

 affords no ground of objection to the opinion, because we see a similar 

 process, though on a widely-different scale, take place in the formation 

 of the medullary cavities and cancelli (vid. infra). It would appear to 

 me, that currents of the nutritive fluid in the bone were chiefly concerned 

 in this further development of the canaliculi; and the more so, because 

 the first rudiments of the canaliculi, like the pore-canals of lignifying 

 plant-cells, manifestly indicate nothing more than the points at which 

 the ossifying cartilage-cells continue to admit and emit fluid; on which 

 account, also, their direction is principally towards the internal and ex- 

 ternal surfaces of the bone, from which the nutritive plasma is derived. 

 It appears to me highly probable, that after the complete ossification of 

 the cartilaginous tissue, the nutritive fluid derived from the blood-vessels 

 of the periosteum and of the medullary cavities (1.) finds new ways for 

 itself towards the lacuna? and their prolongations, which, as it may be 

 said, alone are still open to it, and in this way effects their opening on 

 the internal and external surfaces of the bone, and (2.) also burrows 

 passages from the cavities lying nearest to it, and thus ultimately pro- 

 duces a ramification of them, and brings about numerous communications 

 between the different cavities. In accordance with which, a secondary 

 formation of canaliculi must take place, not only in the region of the 

 thickened walls of the original cells, but also in the osseous matrix, and 

 this to a considerable extent, as is at once evident, when the distances 

 between the anastomosing cavities are compared with the diameter of 

 the original cartilage-cells. 



The development of the medullary spaces (cancelli) and of the medulla, 

 is to a certain extent the last act in the transformation of cartilage into 

 bone. The medullary spaces do not arise in a coalescence of the cartilage- 

 cells, but from a solution of the more or less perfectly formed bone-sub- 



