CHAPTER VIII 

 MOTION AND LOCOMOTION 



The Special Physiology of the Muscles. Having now con- 

 sidered separately the structure and properties in general of the 

 skeleton, the joints, and the muscles, we may go on to consider 

 how they all work together in the Body. Although the properties 

 of muscular tissue are everywhere the same, the uses of dif- 

 ferent muscles are very varied, by reason of the different parts 

 with which they are connected. Some are muscles of respiration, 

 others of deglutition; many are known as flexors because they 

 bend joints, others as extensors because they straighten them. 

 The exact use of any particular muscle, acting alone or in concert 

 with others, is known as its special physiology, as distinguished 

 from its general physiology, or properties as a muscle without refer- 

 ence to its use as a muscle in a particular place. The functions 

 of those muscles forming parts of the physiological mechanisms 

 concerned in breathing and swallowing will be studied here- 

 after; for the present we may consider the muscles which co- 

 operate in maintaining postures of the Body; in producing move- 

 ments of its larger parts with reference to one another; and in 

 producing locomotion or movement of the whole Body in space. 



In nearly all cases the striped muscles carry out their functions 

 with the cooperation of the skeleton, since nearly all are fixed 

 to bones at each end, and when they contract primarily move 

 these, and only secondarily the soft parts attached to them. To 

 this general rule there are, however, exceptions. The muscle for 

 example which lifts the upper eyelid and opens the eye arises 

 from bone at the back of the orbit, but is inserted, not into bone, 

 but into the eyelid directly; and similarly other muscles arising 

 at the back of the orbit are directly fixed to the eyeball in front 

 and serve to rotate it on the pad of fat on which it lies. Many 

 facial muscles again have no direct attachment whatever to bones, 

 as for example the muscle (orbicularis oris) which surrounds the 

 mouth-opening, and by its contraction narrows it and purses out 



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