INTRODUCTION. 9 



cle. In animal bodies there are as many different muscles as 

 there are simple movements ; and besides, there are generally, 

 for the purpose of bringing back the parts to their original posi- 

 tion, other bundles of fibres destined to produce a contrary ef- 

 fect, and which have been accordingly termed antagonist mus- 

 cles. The element of the muscular fibre, chemically consider- 

 ed, appears to reside in a matter called Jibrine. 



The other organs destined to the purposes of movement are 

 altogether passive. Sometimes they are disposed outwardly 

 under the appearance of membranes or integuments more or less 

 solid, sometimes under the form of crusts or sheaths, in the in- 

 terior of which the muscles are placed. The solidity of these 

 parts, their structure, their articulation, and movements, corre- 

 spond to the animal's mode of life ; and these crusts, shells, scales, 

 or sheaths, are of a calcareous or horny nature, and adapted to 

 the efforts they are destined to sustain, the.more soft coverings 

 of this kind, as may be conceived, being only calculated for mo- 

 tion in fluids. 



In the higher classes of animals the solid articulated parts 

 which form the frame-work of the body and modify its form are 

 almost always placed internally, and serve the purpose of joint- 

 ed levers, and as a fulcrum for their muscular coverings. These 

 parts are the bones of animals, and when arranged as a whole 

 they are termed the bony skeleton. All these bones meet in a 

 central stalk, or hollow and moveable column, called the spine, 

 of which the pieces, more or less solid and numerous, are termed 

 vertebras. Among those which are on this account named Ver- 

 tebrated Animals, the column is terminated at one end by the 

 cranium, a bony cavity inclosing the mass of cerebral matter 

 which gives sensation, and is the seat generally of four organs of 

 sense. In the head is also placed the mouth, an instrument 

 capable of prehension, and provided with organs for mechanical- 

 ly dividing the aliment ; and often also in this important part of 

 animals the organs are placed which produce or facilitate the 

 action of respiration. The spine is generally prolonged behind, 

 and forms the tail in many animals. 



The mechanical apparatus by which animals acquire the 

 knowledge of what is around them are termed organs of sense, 

 and the impressions made on these by external objects, sensa- 



