vn BONE 309 



cylinder with the periosteal sheath of the shaft ; (iv) of a 

 coarse, irregular vascular meshwork occupying at each end 

 the space between the medullary cylinder and the plate 

 of articular cartilage, and connected with the periosteum 

 of the lateral parts of the articular end ; (v) of the hard, 

 perfect osseous tissue which tills the meshes of these two 

 networks. Such is the general structure of all long bones 

 with cartilaginous ends, though some, as the ribs, possess 

 no wide medullary cavity, but are simply cancellated in 

 the interior. In some very small bones even the cancelli 

 are wanting. And there are many bones which have no 

 connection with cartilage at all. 



If a bone is exposed to a red heat for some time in a 

 closed vessel nothing remains but a mass of white "bone- 

 earth," which has the general form of the bone, but is 

 very brittle and easily reduced to powder. It consists 

 almost entirely of calcium phosphate and carbonate. On 

 the other hand, if the bone is digested in dilute hydro- 

 chloric acid for some time the calcareous salts are dissolved 

 out, and a soft, flexible substance is left, which has the 

 exact form of the bone, but is much lighter. If this is 

 boiled for a long time it will yield much gelatin, and only 

 a small residue will be left. Osseous tissue therefore 

 consists essentially of an animal matter impregnated with 

 calcium salts, the animal matter being collagenous like 

 connective tissue. 



A sufficiently thin longitudinal section made by grinding 

 down part of the wall of the medullary cavity of a bone — 

 which has been well macerated in water and then 

 thoroughly dried — if viewed as a transparent object with 

 a magnifying glass, shows a series of lines, with dark 

 enlargements at intervals, running parallel with the 

 Haversian canals. If the section, instead of being longi- 

 tudinal, were made transversely to the shaft, and there- 

 fore cutting through the majority of the Haversian canals 

 at right angles to their length, similar lines and dark 

 spots would be seen to form concentric cu'cles at regular 



