MUSCLES. 



CHAPTER IX. 



OF MUSCLES. 



THE muscles of man, and indeed of all the mammalia, birds, 

 and fishes, constitute by far the greatest part of the body. They 

 are the organs of motion, and constitute what in common lan- 

 guage is called jflesh. In man, the muscles are divisible into two 

 kinds, 1. Those which are attached to the bones, and 2. Those 

 of the viscera. The former, a few excepted, have a red colour 

 in warm-blooded animals, but are white in the greater number 

 of fishes. The latter are annular, as in the intestinal canal and 

 urinary bladder. They are usually pale, if we except the heart, 

 the muscles of which have the same colour as those attached to 

 the bones. 



The muscles consist of a congeries of fibres, usually parallel 

 to each other. Each of these fibres, when viewed under the mi- 

 croscope, is composed of a number of smaller fibres, and the 

 smallest fibres of all, or what may be called the element of the 

 muscle, was believed by Leuwenhoek to be a congeries of sphe- 

 rical molecules, applied to each other so as to constitute a thread,* 

 and this opinion has been confirmed by subsequent observers. 

 These globules consist of fibrin. Every muscular fibre is en- 

 closed in a very delicate sheath of cellular substance, A num- 

 ber of these fibres associated together is covered and held toge- 

 ther by another delicate sheath of the same cellular substance. 

 Several of these are in their turn enveloped in a new common 

 sheath of the same substance. Thus, the whole muscle is com- 

 posed of numerous muscular fibres collected together in bundles, 

 and held together by connecting cellular substance. Hence it is 

 easier to tear these fibres from each other than to break them in 

 a direction perpendicular to their length. 



The 'structure of muscle has been investigated with much care, 

 by Mr Skey,f who has confirmed the statements of Messrs 

 Hodgkin and Lister, that the ultimate filaments of muscle are 

 not composed of globules, but are hollow tubes, the size of which 

 does not exceed I7 ^^th of an inch. They are collected into 



* Phil. Trans. 1677, Vol. xii. p. 899. f Phil. Trans. 1837, p. 871. 



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