130 ZOOLOGY. 



In the lowest animals the muscles are all connected with, 

 and dependencies of, the integument, which is soft and 

 flexible, and by acting on this, they move the body in whole 

 or in part ; but in animals of a more perfect structure, the 

 motor apparatus becomes more and more complex, and is 

 formed not only of muscles, but of a skeleton, itself com- 

 posed of solid parts calculated to augment the precision, the 

 extent, and the force of the movements, to protect the viscera 

 against external violence, and to determine the general form 

 of the body. 



260. This framework or skeleton, to which the muscles 

 are chiefly attached, is in man, and all animals called verte- 

 brate, situated internally, and is covered by the soft parts. 



In some fishes (as in the skate) the skeleton is formed of a 

 white, opaline, compact, homogeneous substance, at once very 

 resisting and elastic. It is called cartilage. In all animals, 

 when very young, the skeleton is at first cartilaginous ; but 

 this condition, which is permanent in certain fishes, is only 

 transitory in the greater number of animals, and the carti- 

 laginous pieces soon become charged with calcareous salts, by 

 which they become firm, hard, comparatively brittle : in this 

 state they are called bones. 



261. Of the Bones. To prove the presence of cartilage 

 as the basis of all bones, all that is required is to immerse a 

 bone in dilute muriatic acid, which, dissolving the calcareous 

 part, leaves a cartilage of the precise form and dimensions of 

 the bone itself. According to Berzelius, the bones of the 

 human skeleton are composed of cartilage, 32* 17; vessels, 11*3 ; 

 phosphate of lime, with a little of the fluorate of calcium, 

 53*04; carbonate of lime, 11*30; phosphate of magnesia, 

 1*16 ; soda, with a little of the chlorine of sodium, 1*20 in 

 100*00 parts. The same chemist found the bones of the ox 

 to be similarly composed, but with much less carbonate of 

 lime. Thus bones by boiling afford much gelatine. 



The ossification of the skeleton commences with various 

 osseous points in the cartilages; these are called nuclei or 

 germs. In youth they are numerous, but they gradually 

 coalesce; thus the femur, in a young person composed of 

 five distinct portions, is at last formed of one. In the lower 

 vertebrate animals many of those remain distinct which in 

 the higher coalesce or become fused. 



The surface of bone is covered with a cellulo-fibrous and 

 vascular membrane, called periosteum. The bones themselves 



