SECT. 104.] OSSEOUS SYSTEM. 201 



layers, of which only the latest remain more in their original 

 form as the compact substance of these bones. 



As is sufficiently apparent from what has been said, the Ha- 

 versian canals arise not like the medullary spaces of the primary 

 osseous substance, formed from ossified cartilage by a solution of 

 existing tissue, but are cavities which have been left from the com- 

 mencement in the periosteal layers. They are, at an early period, 

 of relatively great size, and their lamellar systems are likewise 

 developed without the co-operation of cartilage. These lamellae 

 are nothing but successive deposits from the soft substance in the 

 canals, which, as was already mentioned, entirely agrees in its fibres 

 and cells with the sub-periosteal ossific blastema, and is, so to 

 speak, only the unossified remains of it. These points may be easily 

 observed in young bones, in which the periosteal layers, before 

 they have been opened up by partial resolution, become more and 

 more compact by means of these new secondary lamellae ; but also 

 in later periods, a more or less ossified blastema (always without 

 calcareous granules) may very frequently be perceived upon the 

 walls of the canals in question. Whilst the vascular canals thus 

 generally become narrowed by secondary depositions, which, as in 

 the periosteal deposits, appear stratified — because either the ossi- 

 fying blastema is stratified or pauses ensue at definite periods in 

 the deposition of the bone — some of them, on the other hand 

 subsequently become widened by absorption, as, for example, the 

 canales nutritii, the larger openings for the vessels upon the apo- 

 physes, many nerve-canals, etc., and, as already remarked, the 

 compact substance is, in many places partially, in some even 

 entirely absorbed. 



The formation of bone upon the inner side of the periosteum, is a thing 

 that has long been known, still it -was hitherto the general opinion, that here 

 also a thin layer of cartilage was concerned in it, until Skarpey and I proved 

 the contrary. Virchow is of opinion that the ossific blastema arises from a 

 luxuriant growth of the periosteum, and that its cells originate by a suc- 

 cessive multiplication of the plasm-cells, whilst the fibrous matrix between 

 them is simply an intercellular substance produced without the influence of 

 cells from the fibrous substance of the periosteum. I, on the other hand, 

 hold, that a layer of cells always exists upon the inner side of the periosteum, 

 from which, by continual growth and multiplication, partly the ossifying 

 cells proceed, partly others, which are metamorphosed with the fibrous 

 matrix of the ossifying blastema. 



The deposition from the periosteum, exhibits a certain contrast to the 

 osseous substance which is developed from cartilage. The former principally 

 forms the compact crust of the cartilaginously pre-formed bones, and is cha- 

 racterised by the presence of Haversian canals and their lamellar systems, 



