234 SOLID PARTS OF ANIMALS. 



more numerous ; because various bones, at first separate, gra- 

 dually unite into one as the age of the individuals advances. 

 They are very various in their shape. Some, as the shoulder- 

 bone, the thigh-bone, &c. are long and hollow ; others, as those 

 of the cranium, are flat and thin ; while others, as those of the 

 wrist and heel, are short and solid, or nearly so. They are cover- 

 ed by an external membrane, which adheres to them closely, and 

 called the periosteum. The external cavity of the long bones is 

 also lined with a periosteum, from which many of the vessels des- 

 tined to nourish the bones originate. The flat bones are hard 

 and dense at the surface, but interiorly they have a kind of ca- 

 vity divided into innumerable cells by means of thin bony parti- 

 tions. 



When bones are stripped of their periosteum by long boiling, 

 they are white, if from a healthy animal. When the animal has 

 been diseased, the bones frequently have a shade of yellow. The 

 specific gravity varies a little : that of the blade-bone or scapula 

 of an ox is 1-656, as determined by Mr John Caswell.* 



The following little table exhibits the specific gravity of various 

 bones as determined by me : 



Os femoris of a sheep, . . 2-0345 



Tibia of sheep, . . . 2-0329 



Ileum of an ox, . . . 1*8353 



Human os humeri, . . . 1-7479 



Vertebra of haddock, . . 1-6350 



First phalanx of human great toe, . 0-9775 



As the age of these bones was unknown, it is impossible to draw 

 any general inference from these experiments. The lightness of 

 the bone of the great toe was obviously owing to the cavity with- 

 in. When boiled in water, they do not lose their shape, but a 

 quantity of collin is separated, and likewise a portion of fatty 

 matter. Alcohol and ether, when digested on bones, also dis- 

 solve a quantity of fatty matter. When left in contact with mu- 

 riatic acid the earthy matter of bones dissolves, and a cartilage re- 

 mains, soft and flexible, but retaining nearly the shape and bulk 

 of the original bone. When this cartilage is boiled for a long 

 time in water, it is dissolved and converted into collin, with the 

 exception of a small portion of fibrous-looking matter, which still 



Phil. Trans. 1693, xvii. 694. 



