GENERAL PRINCIPLES APPLICABLE TO 



medullary canal; while a certain number terminate in the areol^e of the 



spongy substance. 



The walls of these canals are constituted by several concentric lamellae 

 p. of fundamental substance, and in 



the body of these are lodged the 

 essential elements of the bony 

 tissue, or osteoplasts (corpuscles or 

 lacunce). These are minute cavi- 

 ties lined by a cellular membrane, 

 and furnished, at their circum- 

 ference, with a great number of 

 canaliculated 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 thig a pp earance has led some ob- 



section cut transversely to the direction of the 

 Haversian canals. 



1, A Haversian canal surrounded by its concentric 

 lamella} ; the lacunae are seen between the la- 

 mellae, but the radiating tubuli are omitted; 

 2, Ibid, with its concentric laminae, lacunae, and 



them, at the upper part, several very long 

 lacunae with their tubuli. 



servers to suppose that they were 

 formed of small masses of calca- 

 reous matter. It is now well 

 known that they are minute 

 cavities, lodging a cell 



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 areolse of 

 this tissue. 



As a rule, the proper tissue of 

 the bones is composed of a frame- 

 work of organic matter which has 

 gelatine for its base, and in which 

 are deposited the calcareous phos- 

 phates and carbonates, which 

 to this tissue iti 

 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. 



OR OSTEOPLASTS OF OSSEOUS SUBSTANCE, 



magnified 500 diameters. 

 a, Central cavity ; 6, Its ramifications. 



