CHAPTER III. 



MUSCULAR AND SKELETAL SYSTEMS. 



We have seen (page 26) that four systems are con- 

 cerned with the distinctive functions of animal life, viz., 

 the nervous system, the sense organs, the muscular sys- 

 tem, and the skeletal system. We have finished the first 

 two. We now take up the second two. 



The object of both these is to produce motion. But 

 motion is coextensive with life, and therefore not pecul- 

 iar to animals. What is really characteristic of animals, 

 except the very lowest, is the use of a peculiar apparatus 

 of nerve and muscle to give greater efficiency to the 

 motion. In the lowest animals we have only general 

 sensibility and general contractility. As we rise in the scale 

 nerve and muscle are introduced, but not yet skeleton. 

 The muscle acts directly on the body to give motion and 

 locomotion. Only in animals somewhat advanced in the 

 scale the skeleton is introduced to give greater velocity 

 and precision to the motion. 



SECTION I. 



Muscular System. 



We have already explained the tissue called muscular. 

 Its one property is that it contracts under stimulus of 

 any kind. Now, a muscle, as an organ, is composed of 

 an aggregation of several tissues, of which the muscular 

 is most abundant and characteristic. But besides mus- 



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