14 



',/ \I:RAL PRINCIPLES APTI.K .\in.E TO 



medullary canal; while a certain number terminate in the arcol of the 



spongy substance. 



Tin- \\iills of those canals are constituted by several concentric lumcllfe 



of fundamental substance, iunl in 

 the body of these are lodged the 

 essential elements of the bony 

 tissue, or osteoplasts (corpuscles or 

 Ittriiitir). These are minute 

 ties lined by a cellular membrane, 

 and furnished, at their circum- 

 ference, with a great number of 

 caualiculatcd prolongations, which 

 communicate with the adjacent 

 osteoplasts, or with the Haversian 

 canals. In a thin dried section 

 of bone, the osteoplasts appear 

 black by transmitted light, and 

 white and brilliant by direct light : 



MINUTE STRUCTURE OF BONE, as shown in a thin tuig appeumncc has led some ob- 



Hcinr en5ely to the direction of the to mpp o ** th cy 



1, A Haversian canal surrounded by its concentric formed of 8ma11 ma8 868 of call "i- 



himella! ; the lacuna are seen between the la- T6OUS matter. It 18 HOW Well 



mellae, but the radiating tubuli are omitted ; known that they are minute 



2, Ibid, with its concentric laminae, lacunae, and ram ifyi n g cavities, lodging a cell 



them, at the upper part, several very long 

 lacuna; with their tubuli. 



Fig. 8. 



with liquid. 



-In the spongy texture no 

 Haversian canals can be seen ; 

 the osteoplasts are irregularly 

 disposed in the thickness of the 

 fundamental substance, which con- 

 stitutes the septa of the areolee of 

 this tissue. 



As a rule, the proper tissue of 

 the bones is composed of a frame- 

 work of organic matter which lias 

 gelatine for its base, and in which 

 are deposited the calcareous phos- 

 phates and carbonates, which give 

 to this tissue its characteristic 

 hardness. This is easily rendered 

 evident by immersing any bone in dilute nitric or hydrochloric acid ; acids 

 dissolve the calcareous salts, but do not act upon the organic framework. 

 So it is that, after some days' maceration, the bone becomes flexible, like 

 cartilage, and loses part of its weight, although it preserves its volume. 

 The counterpart of this experiment may be made by submitting it to the action 

 of fire. It is then rendered quite friable, because its organic skeleton has 

 been destroyed without the earthy salts it contained being affected. 



Periosteum. This is a very vascular and nervous fibrous membrane that 

 covers the entire bone, with the exception of the articular surfaces. Its 

 thickness and adherence are not the same everywhere. By its inner face it 

 corresponds to the surface of the bone; by its external face, it is confounded 

 with the insertion of the tendons and ligaments, or with the surrounding 

 connective tissue. 



LACUN.fi, OR OSTEOPLASTS OF OSSEOUS SUBSTANCE, 



magnified 500 diameters, 

 a, Central cavity ; 6, Its ramifications. 



