ON M OSCULAR ACTION. 99 



size of the cavity of the belly, and thus not only 

 assists the natural evacuations, but co-operates in 

 the function of respiration. 



In contemplating this arrangement, it is impossi- 

 ble not to be struck with the consummate skill with 

 which every act of every organ is turned to account. 

 When the chest is expanded by a full inspiration, the 

 bowels are pushed downwards and forwards to make 

 way for the lungs ; when the air is again expelled, 

 and the cavity of the chest diminished, the very 

 muscles i i t, which effect this by pulling down the 

 ribs, contract upon the bowels also, and push them 

 upwards and inwards, as can be plainly perceived 

 by any one who attends to his own breathing. By 

 this contrivance, a gentle and constant impulse is 

 given to the stomach and bowels, which is of great 

 importance to them in contributing to digestion and 

 in propelling their contents ; and One cause of the 

 costiveness with which sedentary people are so 

 habitually annoyed is the diminution of this natural 

 motion in consequence of bodily inactivity. 



From the preceding exposition, the action of the 

 muscles a, k, /, which bend the arm and forearm, 

 will be easily understood, and some notion may be 

 formed of the innumerable combinations into which 

 a system composed of upwards of 400 pieces may 

 be thrown, in effecting all the movements required 

 from the human frame. In some of the operations 

 in which we engage, nearly the whole, and in others 

 only a part, of the muscles are thrown into action 

 at one time. The simultaneousness of action which 

 obtains in such instances, and which occurs in 

 almost every act of life, however simple, and with- 

 out which no dictate of the will could be harmoni- 

 ously and successfully obeyed, depends solely on 

 the distribution and connexions of the nerves which 

 animate the muscles. Every individual fibre of 

 every muscle is supplied with nervous filaments, and 

 different fibres of the same muscle are indebted for 



