THE OSSEOUS SYSTEM. 301 



§ 105. 



Elementary processes in the Layers formed from the Periosteum. 

 — The periosteum of the primarily cartilaginous bones, i.s propor- 

 tionally very thick and vascular, consisting, as early as at the fifth 

 mouth, of common connective tissue and fine elastic filaments, 

 the latter of which in process of time become stronger and 

 stronger, occasionally assuming the nature of elastic fibres. On 

 the inner aspect of this fully formed periosteum, there is now 

 deposited an ossijic blastema firmly adherent to the bone 



by a thick coat of more or less granular, calcareous matter, may indeed often be ob- 

 tained free; but they arise, like the corresponding bodies in rickety bone, simply 

 from the deposition of calcareous matter in the cartilage-cavity before it has taken 

 place in the matrix, or from a want of union between the two deposits ; and are 

 therefore quite accidental. 



The lacuna are developed, according to these authors, by the shooting out of the 

 granular cells into processes, and their direct conversion into the lacuna, the nucleus 

 of the granule-cell remaining as the nucleus of the lacuna. On this point also, we 

 must ditfer from them, and agree with Virchow (1. c, note, § 101) and Kblliker 

 {supra, § 104), that the development of the canaliculi is, by a process of resolution, 

 quite independent of the corpuscles, which simply diminish in size, and either remain 

 as the so-called " nuclei" of the lacuna: or totally disappear. We can especially 

 recommend the Skate (fig. 136 A, 2) as a subject in which to trace the process of 

 formation of lacunae, as the bone is homogeneous and transparent, and in consequence 

 of being inclosed in a large mass of firm cartilage, may lie cut with ease into very 

 thin sections. We have observed it with great clearness also in enehondroma. 



There is one argument which seems to us conclusive on this point. Wherever the 

 canaliculi can be seen at all, however young the tissue, they are perfectly clear and 

 transparent. If, however, they were formed by processes of the granular cells, they 

 ought to be granular, and more or less opaque. 



Taking the same view of the structure of cartilage as Messrs. Tomes and 

 De Morgan, then, our view of the nature of the lacunae, resulting from its ossifica- 

 tion, agrees with that of Professor Kblliker. Cartilage becomes bone by the deposit 

 of calcareous salts in the matrix, and occasionally in its cavities. The lacunae are 

 spaces left round the corpuscles, from which, by resorption, processes — the canaliculi, 

 — are subsequently developed. If it be asked how it is that the lacunas may fre- 

 quently be demonstrated both optically and chemically as distinct bodies, we must 

 call to mind the fact already referred to, that in cartilage, the walls of the cavities 

 have frequently undergone less change than, or a different change from, the surround- 

 ing matrix ; and therefore appear both optically and chemically distinct, though they 

 are by no means so, morphologically : and, therefore, that there is no difficulty in 

 supposing the same thing to occur in bone. The chemical differentiation of the wall 

 of the lacuna is, in fact, exactly comparable to that of the wall of the cavity which 

 contains the " nucleus" in connective tissue, and in fibro-cartilage ; and which gives 

 rise to the formation of the elastic element in those tissues. — Eds.] 



