MUSCLES OF THE HUMAN BODY. 347 



Nervous Influence. The contractility, as well as the 

 irritability, of the muscles, depend on the nervous influ- 

 ence. Thus, if the brain is compressed, so that the will 

 is destroyed, all action in the voluntary muscles ceases. 

 The involuntary muscles, as those of the heart, and res- 

 piration, may continue for a time, under such circum- 

 stances, but the person lies as if in the arms of death, 

 so far as the movement of the limbs is concerned ; and 

 if this condition continues, and the nervous power, which 

 depends on the action of the brain, is obstructed for a 

 certain time, the heart ceases to act, and the respiration 

 slops. Of course, if this state be continued for more 

 than a few minutes, death must be the consequence ; 

 but if the pressure from the brain be removed within a 

 certain period, all the muscles of the system regain their 

 wonted activity, and the person, as it were, comes to life, 

 in consequence of the renewed action of the nervous 

 power. 



Irritability is also the consequence of nervous influ- 

 ence, but is not dependent on the will. Hence some of 

 the muscles are *till irritable after the animal ceases to 

 live. Thus, the muscles of criminals, after execution, 

 are again set in motion by a galvanic shock, and the 

 heart of a frog will continue to beat, on touching it with 

 the point of a pin, for hours after it is separated from the 

 animal. 



Having already illustrated the subject of muscular ac- 

 tion at page 227 and onward, we shall here proceed to 

 exhibit, and name the first layer of muscles of the hu- 

 man frame, or those immediately under the skin. The 

 total number of muscles is 527, of which 257 are in 

 pairs, and lie on opposite sides of the body. 



Anterior View of the Muscles of the Human Body, Fig. 6. 



Observation. Some of. the muscles extend from the 

 anterior to the posterior portions of the body, so that, in 

 the two positions here exhibited, a few of them have the 

 same name. It is unnecessary to describe the situation 

 of each muscle, as this will be seen on reference to the 

 figures. 



