THE USE OF MUSCLES IN THE BODY 123 



permanently, and so forcibly that extreme measures must often be 

 adopted to return the part to its normal resting situation. The 

 importance of this constant tension during life is probably in the 

 instant readiness it gives the muscles. There is never any slack 

 to be taken up; motion of the joint is simultaneous with the con- 

 traction of the muscle. 



Functional Muscle Groups. In attempting to analyze the 

 exceedingly numerous and diverse muscular movements of which 

 we are capable we have to bear in mind that in the state of nature 

 for which our bodies were primarily adapted men's movements 

 were directed to fewer and simpler ends. Our fundamental ac- 

 tivities fall into a small number of groups, and we shall see that 

 our more complex movements are but modifications of the funda- 

 mental ones. 



According to this principle we can classify our muscular acts as 

 follows: posture; locomotion; prehension (grasping); mastication 

 (and swallowing); vision; voice production (including breathing). 

 Of these groups posture, locomotion, and prehension are treated in 

 following paragraphs. A separate chapter is devoted to voice 

 production (Chap. XXXIII). The others are treated in detail in 

 connection with the discussion of the particular bodily functions 

 with which they are associated. Some points of general interest 

 concerning them may not be out of place here. Among the facial 

 muscles are found groups devoted to mastication; to vision; to 

 voice production; and to prehension. The masticatory and visual 

 muscles do not show in man any very striking differences from their 

 functioning in other mammals. Prehension, which in man and 

 the higher monkeys is taken over so largely by the front limbs, 

 manifests itself among the facial muscles in the grasping power of 

 the very flexible lips, which are in most of the lower mammals 

 important grasping organs, but in man confined chiefly to the safe 

 guidance of food into the mouth. 



The tongue is a muscular mass composed of several distinct mus- 

 cles which are interwoven in such a manner that by their interac- 

 tion they can draw, thrust, or twist the organ into the numerous 

 positions and shapes it is capable of taking. The larger tongue 

 muscles have a bony attachment at one end, either in the hyoid 

 bone (p. 62) or the lower jaw. Their insertions are within the 

 fleshy mass itself. There are besides these large muscles a number 



