OF THE MUSCULAR SYSTEM IN GENERAL. 427 



impossible to answer these questions, or to choose between 

 these hypotheses with any reasonable motive of preference. 

 684. The, effects of muscular actfcn in the living body 4 are 

 to produce or to prevent the movement of the solid and liquid 

 parts, or even of the whole body, as the case may be. 



The modes according to which the muscles exercise their 

 action, may be reduced to two: 1. The two extremities of the 

 fibres in action may remain equally stationary, as in the ac- 

 tion of the diaphragm, the muscles of the abdomen, the bucci- 

 nator, &c.; or be equally moveable, as in the sphincters, the 

 annular fibres of the stomach, the intestines, &c.; 2. One ex- 

 tremity of the fibres in action is more fixed than the other, so 

 that the more moveable one is (frawn towards the other, as in 

 the greater part of the muscles of the members;' particularly in 

 those of the fingers and toes; or else one extremity is abso- 

 lutely stationary, and the other absolutely i&oveablej as in the 

 muscles of the eye, the soft palate, &c. 



685. The actions of the muscles that naturally take place 

 in the body, may be divided into two classes: voluntary and 

 involuntary. 



The voluntary actions are those of all the muscles that ser.ve 

 the purpose of the skeleton both when stationary or in motion, 

 that contribute to the movements of the larynx, and to those 

 of the organs of sensation. All these muscles receive their 

 nerves directly from the spinal marrow. 



The involuntary actions may be subdivided into three or- 

 ders; some are produced by the stimulus acting across a thin 

 membrane which immediately covers the muscles; such are 

 the movements of the alimentary canal, of the bladder, of the 

 heart, &c. ; others are produced by stimuli of an analogous 

 kind, but which are propagated by means of a connexion with 

 many other muscles: such are the movements of deglutition, 

 respiration, coughing, sneezing, fecal excrementation, emis- 

 sion of sperm, urinating, accouchement, &c. The others are 

 the movements of emotion or passion, such as laughing, cry- 

 ing out, &c. 



Among the actions or movements of this second class, some 

 have been considered as semi-voluntary, or .as constituting an 



