108 PHILOSOPHY OF ZCOLOGY. 
1. Periosteum.—This bears the same relation to the bone 
as the skin to the body, serving as a covering for its surface, 
and a sheath for the different cavities which enter it. It 
varies in thickness, according to the nature of the bone. Its 
texture is obviously fibrous ; and it possesses bloodvessels. 
Its sensibility mdicates the existence of nerves. Where 
this organ covers cartilaginous processes, it is called Peri- 
chondrium. 
2. Cartilaginous basis.—This part of bone apparently 
consists of gelatine and coagulated albumen. The gelatine 
may be obtained by boiling the bone, previously broken in- 
to small fragments, for a considerable time in water. If the 
liquor be sufficiently concentrated, it will gelatinize when 
cold. The coagulated albumen may be obtained, by 
removing the earthy salts by means of weak muriatic acid. 
What remains is termed cartilage. It retains the original 
figure of the bone; and may be considered as the frame, in 
the cells of which the earthy matter has been deposited. It 
contains numerous bloodvessels, which reach it by passing 
through the periosteum. 
3. Earthy Matter—The quantity of earthy matter may 
be ascertained, by exposing the bones for some time to a red 
heat. The cartilaginous basis is consumed, and the earthy 
matter is left behind ; or the earthy matter may be obtain- 
ed in solution, by steeping the bone in diluted muriatic 
acid. It chiefly consists of lime united with phosphoric acid, 
forming phosphate of lime. Carbonate of lime occurs, but 
generally in small quantity. Phosphate of magnesia is like- 
wise found, sometimes to the amount of 3 per cent. Har- 
cHETT detected a minute portion of sulphate of lime ; and 
BerzeE.ivus has confirmed the observation of other experi- 
mentalists, as to the occurrence of fluate of lime to the extent 
of 3 per cent. 
4, Fat.—This part of bones bears a close resemblance 
to the fixed oils. In some bones, as those of whales, it oc- 
