94 THE COMMON FROG. [chap. 



CHAPTER VII. 



THE MUSCLES OF THE FROG. 



We may now pass to the consideration of some points 

 exhibited by another set of structures — namely, the 

 muscles. 



The muscles of an animal constitute its flesh, which 

 as the most ordinary inspection shows us, is composed 

 of different portions of soft fibrous substance, such 

 portions being separated from one another by inter- 

 posed layers of membrane. Each such portion, so 

 separated, is a muscle, and is attached at its two 

 ends to two parts (bones or what not), which may be 

 adjacent or more or less distant. The fibres which 

 compose it have the remarkable property of con- 

 tracting under certain conditions, and, when con- 

 tracted, the whole muscle is shorter and thicker than 

 before, and the two parts to which it is attached 

 become consequently approximated. 



Muscles may be large expanded sheets of flesh (as 

 in the abdomen), or long and more or less narrow, as 

 in the limbs. 



Muscles are said to be "■ inserted," or to " take 

 origin from " the parts to which they are attached, 



