CHAPTER XI. 



MOTION AND LOCOMOTION. 



The Special Physiology of the Muscles. Having now 

 considered separately the structure and properties in gen- 

 eral of the skeleton, the joints, and the muscles, we may 

 go on to consider how they all work together in the Body. 

 The properties of a muscle for example are everywhere the 

 same, but 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, and so on. The 

 determination of the exact use of any particular muscle 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 uses 

 of those muscles forming parts of the physiological mechan- 

 isms 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 parts with reference to one 

 another; and in producing locomotion or movement of the 

 whole Body with reference to its environment. 



In nearly all cases the striped muscles carry out their 

 functions with the co-operation 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 



