254 BONE OR OSSEOUS TISSUE. 



BONE OR OSSEOUS TISSUE. 



The bones are the principal organs of support, and the passive instruments of 

 locomotion. Connected together in the skeleton, they form a framework of hard 

 material, which affords attachment to the soft parts, maintains them in their due 

 position, and shelters such as are of delicate structure, giving stability to the whole 

 fabric, and preserving its shape ; and the different pieces of the skeleton being joined 

 moveably together, serve also as levers for executing the movements of the body. 



While substantially consisting of hard matter, bones in the living body are 

 covered with periosteum and filled with marrow ; they are also pervaded by blood- 

 vessels for their nutrition. 



Bone has a white colour, with a pink and slightly bluish tint in the living body. 

 Its hardness is well known, but it also possesses a certain degree of toughness arid 

 elasticity ; the last property is peculiarly well marked in the ribs. Its specific 

 gravity is from 1.87 to 1.97. 



Chemical Composition. Bone consists of an earthy and an animal part, inti- 

 mately combined together ; the former gives hardness and rigidity, the latter tenacity, 

 to the osseous tissue. 



The earthy part may be obtained separate by calcination. When bones are 

 burned in an open fire, they first become quite black, like a piece of burnt wood, 

 from the charring of their animal matter ; but if the fire be continued with free 

 access of air, this matter is entirely consumed, and they are reduced to a white, 

 brittle, chalk-like substance, still preserving their original shape, but with the loss of 

 about a third of their weight. The earthy constituent, therefore, amounts to about 

 two-thirds of the weight of the bone. It consists principally of phosphate of lime, 

 with about a fifth part of carbonate of lime, and much smaller proportions of fluoride 

 of calcium, chloride of sodium, and magnesian salts. 



The animal constituent may be freed from the earthy, by steeping a bone in 

 diluted hydrochloric acid. By this process the salts of lime are dissolved out, and a 

 tough flexible substance remains, which, like the earthy part, retains the perfect 

 figure of the original bone in its minutest details ; so that the two are evidently com- 

 bined in the most intimate manner. The animal part is often named the cartilage of 

 bone, but improperly, for it differs entirely from cartilage in structure, as well as in 

 physical properties and chemical nature. It is much softer and much more flexible, 

 and, by boiling, it is almost wholly resolved into gelatin. It may accordingly be 

 extracted from bones, in form of a jelly, by boiling them for a considerable time, 

 especially under high pressure. 



The lining membranes of the Haversian canals and the walls of the lacunae are formed of 

 a material which resists the action of strong hydrochloric acid (which dissolves the remainder 

 of the animal matter) (Langer). 



In the compact substance of a femur that had been long buried. Aeby found only 16'5 per 

 cent, of animal matter. 



The fluoride of calcium is found in larger quantity in fossil than in recent bones. 



MINUTE STRUCTUBE OF BONE. 



On sawing up a bone, it will ba seen that it is in some parts dense and close in 

 texture, appearing like ivory ; in others open and reticular ; and anatomists accord- 

 ingly distinguish two forms of osseous tissue, viz., the compact, and the spongy or 

 cancellated. On closer examination, however, especially with the aid of a magni- 

 fying glass, it will be found that the bony matter is everywhere porous in a greater 



