296 STRUCTURE OF THE SHEEP. 



which the various organs are packed away in their proper 

 cavities is worthy of particular notice. The lungs and the 

 heart are so adapted to the shape of the chest, that there is 

 at no time any vacant spot ; and the more numerous contents 

 of the abdomen are so disposed, that while each has suffi- 

 cient freedom for the proper performance of its functions, 

 yet the whole are packed away with the most economical 

 care : there is no void whatever to be found. 



SKELETON OR BONY STRUCTURE OF THE SHEEP. 



The skeleton of animal bodies is formed of bone, a sub- 

 stance possessing firmness and stability for the attachment 

 of muscles, the protection of the vital organs, and the sup- 

 port of the softer parts. It is composed of animal matter 

 and earthy salts ; the former consisting of cartilage, gelatine, 

 and fat or marrow, and the latter of phosphate of lime in 

 considerable proportion, a lesser quantity of carbonate of 

 lime, and a small portion of other salts. The cartilage of 

 bones is formed before the earthy matter, and constitutes, in 

 fact, the nidus in which the latter is deposited. Bones can 

 be freed from their earthy portion by immersion in an acid, 

 by which process the gelatine is also dissolved, and pure 

 cartilage is left, which is elastic, but retains the original fig- 

 ure of the bone. On the other hand, bones, by exposure to 

 a great heat, are deprived of the animal substance, and the 

 earthy part remains. 



The use of the marrow is more particularly to prevent the 

 too great dryness and briitleness of bones. To the animal 

 portion of their composition they are, therefore, indebted for 

 their shape and what degree of elasticity they possess, and 

 from the. earthy portion they derive the important purposes 

 of strength and stability. Thus are these different elements 

 combined together, and by an union of their diflerent princi- 

 ples form a substance admirably adapted for affording full 

 scope for the play of the various organs of life, protecting 

 at the same time the vital parts from external injury, admit- 

 ting and assisting the powers of locomotion, and, in fine, 

 forming a secure fabric for the beautiful building of animal 

 frames. 



Every bone is covered by a membrane called the perios^ 

 teurn^ which also lines the internal cavities and secretes the 

 marrow ; its use is to circumscribe the form of bones and 

 protect them by its tenseness, as well as to afford the medium 



