100 MOTIONS OF ANIMALS. 



CHAPTER II. 



OP THE MOTIONS OP ANIMALS. 



'Tim motions performed by animals are of two kinds, 

 voluntary and involuntary. The first are performed at the will 

 of the animaj, are under the direction of its intelligence and 

 judgment, and are suggested by its desires, wants, passions, 

 and affections. Such are the movements of its limbs, and or- 

 gans of sense and voice, by which it moves about from place 

 to place, and maintains a communication with its fellow- 

 beings. The second, or involuntary motions, are placed totally 

 out of the control of its will. It has no influence over their 

 performance, and is not even conscious that they are performed. 

 Of this kind are the motions of the heart, the stomach, &,c. 



' The voluntary motions are performed by the instrumen- 

 tality of bones, articulations, muscles, arid tendons. The 

 bones are connected together by the articulations or joints, 

 which are so constituted as to admit of the moving of one 

 upon the other, like a hinge, as in the knee, or like a ball and 

 socket, as in the hip and shoulder. The muscles are fleshy 

 bodies of various lengths and sizes, formed of fibres, and ter- 

 minated by tendons. These last are white and very strong 

 cords, usually called sinews, by which the muscles are at- 

 tached to the bones. The muscles have the power of short- 

 ening or contracting themselves ; and in consequence of a 

 diminution of their length, the bones to which they are fixed 

 are moved upon their articulations in different directions, ac- 

 cording to the situation of the muscle. And by the combined 

 operations of a great many muscles, all the various motions 

 of the bodies of animals are performed. Thus, in mastication, 

 the under jaw is, by the contraction of one set of muscles, 

 drawn upwards with great force, so that the lower teeth are 

 made to crush and grind the food against the upper ; this 

 contraction continues but for a moment ; the muscles are re- 

 laxed, and by another set of them, the jaw is drawn down- 

 ward. This motion is repeated as long as we continue eat- 

 ing. This motion is more simple than that of most of our 

 limbs, but they are all performed upon the same general prin- 

 ciple of muscular action.' 



( The muscles compose a great part of the bodies of most 



