16 



PHYSIOLOGY. 



making known their ideas among themselves by articulate 

 sounds or by cries. 



This faculty is called the voice, and its apparatus the vocal 

 apparatus, or 



Larynx. 



The larynx is attached above to a bone called the os hyoïdes 

 and below to the trachea. Its sides are formed by five carti- 

 lages, and supplied with muscles by which a limited degree 

 of motion is effected : its superior opening is called the glottis, 

 over which is a fibro-cartilaginous substance named epiglottis 

 placed at the base of the tongue. 



The Muscular Apparatus. 



"Muscle" is the term applied to certain fleshy organs 

 composed of fibres of extreme tenuity, which are straight and 

 arranged in a parallel manner among themselves. 



These organs are endowed with contractibility ; that is to 

 say, with the power of shortening and extending themselves 

 alternately. In the motions of contraction the fibres fold up 

 in a zigzag form, and the muscle becomes hard and swollen. 

 The power of the muscles does not act directly on the bones, 

 but through the agency of certain whitish, fibrous prolon- 

 gations, denominated when thick, tendons, and when spread 

 out, aponeuroses. 



Muscular contractions operate, some under the influence 

 of the will (and in this case the muscles receive nerves from 

 the cerebrospinal system) ; others again are produced without 

 any agency on the part of this faculty, and in this case the 

 muscles receive their nerves from the great sympathetic; 

 others, finally, are produced by the united influence of both 

 the nervous systems. 



The Bony Apparatus. (The Skeleton.) 

 Skeleton is the name applied to the whole collection of 

 bones in the superior animals. Its use is to afford a base of 

 support to the soft parts, and to furnish the muscular powers 

 with resisting levers, which give energy, extent and precision 

 to the motions. The bones are the hardest portions of 

 the bodies of animals. Bones are formed of two principal 

 substances ; the one an animal substance (gelatine), inter- 



