ANIMAL MECHANICS. 



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pable of the longest endurance of work. This conclusion 

 agrees with the Table of Mr. Bowman, from which it appears 

 that of all animals the muscles of Birds possess the smallest 

 fibres, and that the muscular fibres of women are smaller than 

 those of men ; for it is well known that no animals are more 

 capable of long-continued muscular exertion and fatigue than 

 Birds; and I have myself found, by direct experiment, that the 

 muscles of women are capable of longer continued work than 

 those of men, although inferior to them in force exerted for a 

 short time.* 



The elementary fibre is encased in a sarcolemma, or sheath, 

 very tough and elastic, but not endowed with the vital pro- 

 perties of the muscular fibre itself ; and, again, many such ele- 

 mentary fibres, each invested by its proper sheath, are united 

 into greater or lesser bundles, separated from each other by 

 areolar tissue, sometimes containing fat, which acts as a lubri- 

 cating medium, to prevent friction between the muscular bun- 

 dles during their rapid and varying action. 



Before speaking of the varieties of origin, insertion, and 

 action of the muscular bundles, it may be useful to say a few 

 words on the distinction between striped and unstriped mus- 

 cles, respecting which there seems to be much confusion of 

 ideas. On examining most muscles with the microscope, they 

 are found to be striped crossways with very delicate and close 

 parallel lines, while other muscles are perfectly free from such 

 an appearance. It is said by some that the distinction of 

 muscles into voluntary and involuntary corresponds with the 

 microscopical distinction into striped and unstriped muscles ; 

 and, if it were not for the all-important exception of the heart, 

 this assertion might be maintained with much appearance of 



* If any man wishes for a simple proof of the inferiority of the endurance of his 

 muscles as compared with those of a woman, let him carry a child on his arm for the 

 same time that his wife or nurse can do with ease, and he will find himself much 

 fatigued. 



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