126 PHILOSOPHY OF ZOOLOGY. 



occasioned partly by the air in the ear, and partly by the 

 motion of the bloodvessels *. 



The changes which take place in the tenacity of muscles 

 after death, are very remarkable. The same force which 

 they could resist with ease, in a living state, is sufficient to 

 tear them to pieces after the vital principle has departed. 

 The tendons, which are sometimes lacerated by the violent 

 contractions of the muscle during life, are much stronger 

 than the muscle itself after death. These circumstances 

 serve to confirm us in the belief of a vital power. If it 

 does not exist, it remains with the mechanical and chemical 

 philosophers to determine, what strengthening principle has 

 departed with life, and whence the weakness of death. 



Muscles, from their mode of action, may be divided into 

 circular and longitudinal. In the circular muscles, the 

 fibres are so arranged, that they contract the part to which 

 they are applied in all its dimensions, as the muscles of the 

 heart and tongue ; or they merely contract the extremity 

 of a tube, so as to close it. In this last case, they are de- 

 nominated sphincters. The longitudinal muscles may be 

 compared to ropes, drawing towards them the objects to 

 which they are attached in a direction influenced by the 

 form of these objects ; and the other muscles acting in con- 

 cert. Where the one extremity of the muscle is attached 

 to a hard part, and the other to a soft, the mechanism is 

 usually of the simplest kind. But where both extremities 

 are fixed to hard parts, which are destined to be used as 

 levers, more complicated machinery is requisite. We have 

 already adverted to the different forms of the joints of the 

 bones suited to different movements. The muscles are 

 fixed to these bones at various angles, and various distan- 



Phil. Trans. 1810, p. 2. 



