240 



DETAILED SYNTHESIS. 

 FIG. 176. 



464. THE TENDONS OF EITHER EXTREMITY OP A MUS- 

 CLE maybe attached to one or to several different points, 

 or to a continuous surface. In one case they are said to 

 have one or several heads or origins, and in the other 

 to have one or several insertions. The head is that ex- 

 tremity that is usually firm, while the insertion is the 

 point or extremity to be moved. 



465. THE USE OF A MUSCLE is, by contraction, to 

 produce motion. 



466. THE CONTRACTION OF A MUSCLE cannot be con- 

 tinued for any considerable length of time ; it must in a 

 short time relax, or lengthen. 



467. THE REASON WHY CONTRACTION CANNOT CON- 

 TINUE is, that decomposition is going on as long as con- 

 traction continues, and as it shuts out the Blood recom- 

 position cannot take place; relaxation must therefore 

 occur in order that the* Blood may have an opportunity 

 of pouring into the muscle, carrying away the used and 

 useless substance, and supplying new material. 



468. Illus. By placing one hand on the front part of the upper 

 arm, and raising and lowering its fore arm, the action of the muscles 

 can be appreciated. When the forearm is raised the muscle shortens, 



464. What said of ? 465. What is - ? 466. What said ? 467. What is 

 468. Illustrate muscular contraction. 



