CHAPTER XL 

 MOTION AND LOCOMOTION. 



The Special Physiology of the Muscles. Having now 

 considered 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 different 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 mus- 

 cle, acting alone or in concert with others, is known as its 

 special physiology, as distinguished from its general physiol- 

 ogy, or properties as a muscle without reference to its use as 

 a muscle in a particular place. The functions of those mus- 

 cles forming parts of the physiological mechanisms concerned 

 in breathing and swallowing will be studied hereafter; for 

 the present we may consider the muscles which co-operate in 

 maintaining postures of the Body; in producing movements 

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

 ducing locomotion or movement of the whole Body in space. 



In nearly all cases the striped muscles carry out their func- 

 tions with the co-operation of the skeleton, since nearly all 

 are fixed to bones at each end, and when they contract pri-' 

 marily 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 



144 



