362 MUSCULAR MOTION. 



CHAPTER II. 



MUSCULAR MOTION, ESPECIALLY LOCOMOTILITY OR VOLUNTARY MOTION. 



THE functions hitherto considered are preliminary to those that have 

 now to attract attention. The former instruct us regarding the bodies 

 that surround us; the latter enable us to act upon them; to execute 

 all the partial movements, that are necessary for nutrition and repro- 

 duction; and to move about from place to place. All these last acts 

 are of the same character; they are varieties of muscular contraction; 

 so that sensibility and voluntary motion, or muscular contraction exe- 

 cuted by the muscular system of animal life, comprise the whole of the 

 life of relation. M. Magendie includes the voice and movements under 

 the same head; but there is convenience in separating them; and in 

 treating the functions of locomotility and expression distinctly, as has 

 been done by M. Adelon. 1 



ANATOMY OF THE MOTORY APPARATUS. 



The organs essentially concerned in this function are the encepha- 

 lon, spinal marrow, nerves, and muscles. The three first of these have 

 been sufficiently described. The last, therefore, will alone engage us. 



Muscles. 



The muscles constitute the flesh of animals. They are distinguished 

 by their peculiar structure and composition; being formed of the ele- 

 mentary or primary fibrous tissue, already described. This tissue has 

 the power of contracting, and thus of moving the parts into which it 

 is inserted; hence, muscles have been termed active organs of locomo- 

 tion, in contradistinction to bones, tendons, and ligaments, which are 

 passive. 



The elementary constituent of the whole muscular system is this 

 primary, fibrous, or muscular tissue, the precise size and intimate texture 

 of which have been the occasion of innumerable researches ; and, as 

 most of them have been of a microscopic character, they are highly 

 discrepant, as a brief history will exhibit. 



Leeuwenhoek 2 asserts, that some thousands of the ultimate filaments 

 are required to form the smallest fibre visible to the naked eye. He 

 describes these fibres as serpentine and cylindrical; and affirms, that they 

 lie parallel to each other, and are of the same shape in all animals, 

 but differ greatly in size. Their size, however, bears no proportion to 

 that of the animal to which they belong. Muys 3 affirmed, that every 

 apparent fibre is composed of three kinds of fibrils, each progressively 



1 Pbysiologie de THomme, 2de edit., ii. 1 & 204, Paris, 1829. 



2 Arcaha Naturae, p. 43. 



3 Investigatio fabricas quas in partibus rausculos componentibus exstat, .p. 274, Lugd. Bat.. 

 1841. 



