THE QSSEOUS SYSTEM. 



though on a widely differenl scale, take place in the formation 



of the medullary cavities and cancclli {rid. infra). It would 

 appear to me, that currents of the nutritive fluid in the bone 

 were chiefly concerned in this further development of the 

 canal icidi ; and the more so, because the first rudiments of the 

 ca/ta/icu/i, like the pore-canals of lignifying plant-cells, mani- 

 festly 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 external 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 produces 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 {cancetti) and of 

 the medulla, is to a certain extent the last act in the trans- 

 formation 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-substance, 

 exactly like the large medullary cavities of the cylindrical 

 bones. This is most distinctly and satisfactorily shown by the 

 examination of the diaphyses of a sound or rachitic bone, but 

 especially in the latter. At the limit of the ossification itself, 

 the osseous tissue for a distance of about i to '.'" is quite 

 compact, without a trace of larger cavities, and is composed in 

 part of the ossified matrix, and in part of cartilage- cells, more 

 or less advanced in their transformation into bonc-eclls ( f Mik. 

 Auat.,' tab. iii) ; beyond this part, however, cavities, at 



