OF THE EXTERIOR MTJSC,L 441 



707. When the interior muscles contract, they sometimes 

 draw into simultaneous and associated action all the exterior 

 muscles which can contrihute to the accomplishment of their 

 function: thus in coughing, sneezing, vomiting, defecation, ac- 

 couchement, &c., a number more or less considerable of mus- 

 cles of the skeleton act by association, with' interior muscles. 

 The interior muscles have no real antagonists like the exte- 

 rior muscles, all their fibres tending to one sole and common 

 end, the diminution of capacity of the cavity which they form. 

 However, we may consider as such, 1st, the foreign substances 

 thai; keep asunder the parietes of the organs formed by these 

 muscles; 2d, the various parts of a particular hollow organ: 

 for example, the auricles with relation to the ventricles; the 

 body of the uterus, and that of the bladder with respect to the 

 neck or orifice of these organs ; 3d, the two muscular layers in 

 the alimentary canal in the peristaltic motion ; the contraction 

 of the longitudinal fibres determining, by pushing forward the 

 faeces, the extension of the annular fibres. Now, there hap- 

 pens in this precisely what takes place in all antagonism: the 

 contraction of one muscle coincides with the relaxation of its 

 antagonist, and vice versa; 4th, finally, the interior muscles 

 find antagonists in the exterior muscles. These muscles have 

 no determined fixed point: those which are annular, contract 

 on themselves; those which are longitudinal, however, have 

 this point in the orifices of the alimentary canal; those of the 

 reservoirs, as the bladder and uterus, as well as those of the 

 heart, have also a fixed point, better determined, in the orifice 

 of these organs. 



SECTION III. 



OP THE EXTERIOR MUSCLES. 



708. These muscles are also called voluntary muscles, mus- 

 cles of animal functions, of animal life, muscles properly so 

 called. It is these that constitute the greater part of the mass 

 of the body. 



