APPLICATIONS OF MUSCULAR POWER. 453 



many Insects strike the air several hundred times, and 

 those of some of the smaller Insects many thousand times, 

 in a second of time. 



Applications of Muscular Power : Bones and Joints. 



595. Muscular contraction performs an important part in 

 nearly every one of the functions of which we have already 

 treated. Thus the reception of the food, and its propulsion 

 along the alimentary canal, forming part of the function of 

 Digestion, are accomplished through its means. The Circula- 

 tion of the blood, again, depends mainly on the agency of a 

 contractile organ, the heart. The Eespiration cannot be kept 

 up, in the higher animals at least, without the aid of certain 

 movements which are accomplished by the muscles. With 

 the processes of Nutrition and Secretion it is not so closely 

 connected ; but the latter is dependent upon it so far as this, 

 that its products are carried out of the body by the aid of 

 muscular contraction. And even in Sensation, the peculiar 

 endowment of muscular tissue comes into use ; by giving to 

 the organs of sense those movements which enable them to 

 take a wider range, and to apply themselves most perfectly to 

 the objects before them. But we have now to study its appli- 

 cations in those general and partial movements of the body, 

 on which depend the locomotion (or change of place) of 

 animals, their attitudes, and a number of other important 

 actions, entirely of a mechanical nature. 



596. The organs by which these are effected, may be con- 

 veniently divided into the active and passive. The active are 

 those which have peculiar vital powers within themselves, and 

 which exert these in giving motion to other parts. To this 

 class, therefore, we refer the Muscles, whose peculiar endow- 

 ments have been just considered. The passive organs, on the- 

 other hand, are those which perform no action of themselves,, 

 which have no power but that of yielding a simply mechanical 

 support, and which consequently perform no movement but 

 such as they are made to do by the muscles. Of this kind 

 are the hard parts which form the skeleton or solid frame- 

 work of the body, whether this be internal or external. 



597. In the lower tribes of animals, the muscles are all 

 inserted in the soft and flexible membrane which covers the 

 body ; and it is by acting upon this, that they can change the 



