Ill 



THE MUSCULAR SYSTEM 



Three kinds of muscle are met with in the 

 animal body. (1) The walls of the alimentary 

 canal and the air-passages, the walls of blood- 

 vessels and other tubular structures contain 

 collections of spindle-shaped muscular cells or 

 fibres whose action is beyond the control of the 

 will. From this circumstance they are known 

 as the involuntary muscles ; and because, 

 microscopically, the individual fibres do not 

 possess a transverse striation, they are said 

 to be unstriped. (2) The chief tissue of the 

 heart is muscular {cardiac muscle), and possesses 

 characters which have caused it to be placed 

 in a class by itself. (3) The voluntary or 

 striped muscles of the body move the various 

 parts of the skeleton, and consist of minute 

 thread-like muscle-fibres, grouped into bundles 

 by sheaths of fibrous tissue. The exterior of 



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