GENERAL PRINCIPLES APPLICABLE TO THE STUDY OF ALL THE BONES. 17 



axis of the bone ; they communicate frequently by transverse branches. "While 

 the most superficial open on the surface of the bone, beneath the periosteum, 

 and the deepest into the medullary canal, a certain number terminate in the 

 areolae of the spongy substance at the 

 ends of the bones. '^" * 



The wails of these canals are con- 

 stituted by several concentric lamellae 

 of fundamental substance, in which are 

 lodged the essential elements of the 

 bony tissue. Each canal, with its 

 vessels, its system of concentric lamellae, 

 its osteoplasts, and its osseous canaliculi, 

 forms a whole (the Haversian system) 

 which represents the complete bone in 

 miniature. All the Haversian systems 

 preserve a certain independence ; the 

 canalicuh of each, after reaching the minute structure of bone, as shown iu a thia 



. , 1 11 n , 1 , section cut transversely to the direction of the 



periphery, are nearly all reflected to- Haversian canals. 



wards the centre (the recurrent canaliculi l, A Haversian canal surrounded by its concentric 



lamellse ; the lacunae are seen between the 

 lamella', but the radiating tubuli are omitted; 

 2, ibid., with its concentric laminae, lacunae, and 

 radiating tuhuli; 3, the area of one of the 

 canals ; 4, 4, intervening lamelljE, and between 

 them, at the upper part, several very long 

 lacunae with their tubuli. 



Fig. 11. 



of Ranvier) and rejoin the canaliculi of 

 the same system, instead of anasto- 

 mosing with those of the neighbouring 

 system. 



Between the Haversian systems, 

 there are the intermediate systems of 

 lamellae which fill the spaces left through 

 the imperfect contact of the former. 

 In all the long bones there is a system 

 of periphercd lamellae, enveloping, ex- 

 ternally, all the Haversian systems ; 

 while a system of perimediiUary lamellce, 

 more or less perfect, also exists at the 

 inner surface of the medullary canal. ^*«^^^^' ^^ '^'''^*?rf ™ °!- ''''f''' substance, 



,,, , ^ , 1-11 magnified 500 diameters. 



Sharpey observed that the peripheral ^^ ^^^^,^1 ^^^-^^ . j^ j^s ramifications, 



bony lamellte were traversed by fibres 



{Sharpey's ov perforating fibres), and J. Renaut has remarked in the same lamellae 

 the presence of elastic fibres. 



The proper tissue of bones is a framework of organic matter which has 

 gelatine for its base, and in which are deposited the calcareous phosphates 

 and carbonates which give to this tissue its characteristic hardness. This 

 is easily rendered evident by immersing any bone in dilute nitric or hydro- 

 chloric acid ; acid 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 and shape. 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. 



B. Periosteum. — This is a very vascular and nervous fibrous membrane which 

 covers the entire bone, with the exception of the articular surfaces and the 



