43 



41. THE BONES, OSSd, 



are hard, dry bodies, of various shapes. United into a moveable 

 framework, which serves as a point of support to the rest of the 

 organs of the body, they form, on the one hand, cavities for their 

 protection, and, on the other, levers to approximate separate 

 organs towards one another, which are set in motion by peculiar 

 contractile organs, the muscles. 



Chemical analysis resolves the osseous mass into the following 

 constituents, abstractedly of the fat, the vessels, &c., found in 

 bone: 



1. Cartilage, the essential, organic part of bone tissue. It consists of cells, 

 contains cavities and tubules, and is only distinguished from permanent car- 

 tilage by the fact that the bone earth is deposited in it, and condenses it. It 

 is obtained by macerating bone in dilute hydrochloric acid. It is soft, flexible, 

 elastic, soluble in a warm solution of Potash, and converted into gelatin by 

 hot water. 



2. Bone earth, which is especially phosphate and carbonate of lime, with 

 some Magnesia and Fluoride of Calcium. 



The proportion of cartilage is about 0*33 ; of the bone earth, 0'G7. The 

 relative proportions dilfer, however, according to age, health, and the bones 

 themselves. 



figure of the bones. Three forms are described : 



1. Long, or cylindrical; 2. Flat; 3. Short, or thick bones. 



1. Long bones, ossa cylindrica, possess a large cavity, occupied 

 by a few cells, and filled with fat and vessels. Externally they 

 are surrounded by compact substance, and they generally serve 

 as levers. The centre part is called body, diophysis ; the ex- 

 tremities, apophyses, are covered with cartilage, and are of the 

 same construction as the short bones. 



2. Short bones, consisting of a spongy mass, formed of deli- 

 cate osseous laminaB connected together: subs, spongiosa, which 

 on the surface is closely compressed, and thus surrounded by a 

 smooth but thin osseous layer, the cortical portion (subs, corti- 

 calis) ; as the bones of the carpal and tarsal articulations. 



3. Flat bones enclose a thin layer of spongy substance, diploe, 

 between two closely approximating planes of solid cortical sub- 

 stance. They form cavities. 



42. Texture of the Bones. 



The spongy and cortical substances consist of narrow cylindri- 

 cal canaliculi, medullary canals [canals of Havers], which form a 

 network, and when they take a determinate course give a fibrous 

 appearance to the bone. They open on one side upon the exter- 

 nal surface, on the other side into the cavity of the bone or the 



