CHAPTER I. 



OSTEOLOGY. 

 STKUCTURE OF BONE. 



Bones are hard, yellowisli- white, insensitive bodies, wliich form 

 the internal or e^icZoskeleton. give attachment to soft structures, 

 and are of various sizes, forms, and densities. In the limbs the 

 bones are usually more or less cylindrical, with expanded 

 extremities, and not only effectually support the body, and 

 afford leverage and attachment to the muscles, but, by uniting,, 

 form the articulations or joints. Where cavities, such as the 

 cranium, chest and pelvis, enclose viscera requiring protection, 

 and support, the bones tend to assume a flat, expanded form. 



Living bone is bluish pink, insensitive, and elastic ; on ex- 

 posure to air it becomes diseased, assumes a black or livid hue, 

 and is extremely sensitive and painful; the teeth excepted, it 

 is harder and of a higher specific gravity than any other animal 

 tissue. Consisting as it does of inorganic salts deposited in a 

 basis of animal matter, to the former it owes its density and 

 hardness, to the latter, its elasticity and tenacity — the union 

 rendering the tissue solid and elastic enough to obviate fracture 

 from ordinary causes. Its components are so intimately blended 

 that, to the naked eye, it appears homogeneous, but, by steeping 

 in dilute hydrochloric, or other strong mineral acid, the earthy 

 matter is dissolved, while the tough flexile animal cast is left. 

 Again, if we expose it to the action of heat we get rid of the 

 animal matter, and a white, brittle, earthy, chalky substance is 

 left, retaining its original shape. 



The relative proportions of animal and earthy matter vary at 

 different periods of life. In the young, the organic constitutes 

 nearly one-half of the bone ; in the adult, it diminishes to about 

 a third, while in old animals it is still less ; hence the bones 

 of very old animals are brittle, and more liable to fracture. 



