FORMATION OF THE TISSUES BONE. 485 



cups are of course converted into closed areoloe of bone, the walls of which are lamelli- 

 form, and at first extremely thin. 



Immediately upon the ossifying surface, the nuclei, which were before closely com- 

 pressed, separate considerably from one another by the increase of material within the 

 cells. The nuclei likewise often enlarge and become more transparent; a condition 

 first pointed out to us by Mr. Tomes. The changes now enumerated may be conve- 

 niently considered to constitute the first stage of the process, which extends only to the 

 ossification 9f the intercellular substance. In this stage there are no blood-vessels 

 directly concerned. 



The areolae or minute cancelli, when first formed, contain only the rows of cells which 

 they have enclosed. It is remarkable, that, when the cartilage is torn from the bone, it 

 usually carries with it one or two layers of these cancelli, or a little more than is repre- 

 sented in Fig. 118. If the specimen be examined deeper in the bone, even at a depth of 

 y'^th or th of an inch, other appearances are met with. The lamellae of bone enclosing 

 the cancelli are no longer simply homogeneous or finely granular in texture, but have 

 acquired more the aspect of perfect bone. They are also thicker, and include in their 

 substance elongated oval spaces, which, excepting that they are of a roughly granular 

 nature, exactly resemble the lacunas of bone already described. They are evidently the 

 nuclei of the cells of the temporary cartilage. They are scattered at pretty uniform dis- 

 tances apart, and they all follow the direction of the lamellae to which they belong. The 

 curvilinear outline of their now ossified cells can often be partially discerned. 



Within the cancelli, only a few cells can be detected, these cavities being chiefly occu- 

 pied by a quantity of new substance, consisting of granules, and resembling a formative 

 blastema or basis, like that out of which all the tissues are evolved. The cells that are 

 met with are in apposition with the wall ; and sometimes one of them seems half ossified, 

 and its nucleus about to become a lacuna. The nuclei of these cells have now always 

 the same direction as the neighbouring lacunas. 



It hence appears that, after the ossification of the intercellular substance, the rows of 

 cartilage-cells arrange themselves on the inner surface of the newly-formed cancelli, and 

 become ossified, with the exception of their nuclei, which remain granular, and subse- 

 quently form the lacunae of bone ; and that a new substance, or blastema, appears within 

 the cancelli, from which, probably, vessels are developed, and the future steps in the 

 growth of the bone proceed. 



The cancelli when first formed are closed cavities. At a subsequent period they ap- 

 pear to communicate, and thus to form the cancelli and Haversian canals of perfect 

 bone; a complete network of blood-vessels becoming developed within them at the same 

 time. 



The subsequent progress of ossification seems to consist essentially of a slow repeti- 

 tion, on the entire vascular surface of the bone, of that process which has been now 

 briefly described. It is probable that new cartilage-cells are developed on that surface, 

 and become ossified in successive layers, their nuclei remaining to form the lacunas, the 

 uniform dispersion of which through bone is thus explained. The cause of the lamina- 

 tion of bone, parallel to its vascular surface, is also thus illustrated. 



The first appearance of pores is in the form of irregularities in the margin of the la- 

 cunas. These increase with the consolidation of the tissue, and are converted into branch- 

 ing tubules which communicate with those adjacent. These pores must consequently 

 be formed in the ossified substance of the cartilage-cells. In our account of the lacunas 

 of perfect bone it was mentioned that, for the most part, those of contiguous Haversian 

 systems do .not communicate across the narrow interval that separates the Haversian 

 rods ; this interval having, in fact, no pores. It results from what has just been said of 

 the mode of deposition of new layers, that the primary osseous net-work, formed in the 

 intercellular substance of the temporary cartilage, must come to constitute the substance 

 intervening between the Haversian rods, the non-porosity of which is thus satisfactorily 

 accounted for, as well as the facility with which the rods themselves may be made to 

 separate from one another. As for the lacunae, their originally granular interior seems 

 to be gradually removed, so that they become vacuities adapted for the conveyance of 

 the nutritious fluids through the compact material* of the perfect bone.* M. C.] 



When the Calcareous matter of Bone has been dissolved away by the action of an 

 acid, the Animal substance which remains is almost entirely dissolved by a short boiling 

 in water; yielding to it a large quantity of Gelatin. This, indeed, may be obtained, by 

 long boiling underpressure, from previously unaltered Bone; and the calcareous matter 

 is then left almost pure. The lime of bones is, for the most part, in the state of Phos- 

 phate, especially among the higher animals; it is curious, however, that in callus ami 

 exostosis, there is a much larger proportion of Carbonate of lime than in the sound bone ; 



* [Tomes in Todd and Bowman, p. 117. 

 41* 



