THE MUSCLES. 95 



for the moistening of the food while the mastication is going 

 on ; glands, to feed the fountains ; a muscular constriction 

 of a very peculiar kind in the back part of the cavity, for 

 the guiding of the prepared aliment into its passage towards 

 the stomach, and in many cases for carrying it along that 

 passage ; for, although we may imagine this to be done 

 simply by the weight of the food itself, it in truth is not so, 

 even in the upright posture of the human neck ; and most 

 evidently is not the case with quadrupeds — with a horse for 

 instance, in which, when pasturing, the food is thrust up- 

 wards by muscular strength, instead of descending of its own 

 accord. 



In the mean time, and within the same cavity, is going 

 on another business, altogether different from what is here 

 described — that of respiration and speech. In addition there- 

 fore to all that has been mentioned, we have a passage 

 opened from this cavity to the lungs for the admission of air 

 exclusively of every other substance ; we have muscles, some 

 in the larynx, and without number in the tongue, for the 

 purpose of modulating that air in its passage, with a variety, 

 a compass, and precision, of which no other musical instru- 

 ment is capable. And lastly, which, in my opinion, crowns 

 the whole as a piece of machinery, we have a specific con- 

 frivance for dividing the pneumatic part from the mechan- 

 ical, and for preventing one set of actions interfering with the 

 other. Where various functions are united, the difficulty is 

 to guard against the inconveniences of a too great complex- 

 ity. In no apparatus put together by art and for the pur- 

 ])oses of art, do I know such multifarious uses so aptly com- 

 bined, as in the natural organization of the human mouth ; 

 or where the structure, compared with the uses, is so simple. 

 The mouth, with all these intentions to serve, is a singk 

 cavity, is one machine, with its parts neither crowded nor 

 confused, and each unembarrassed by the rest — each at least 

 at liberty in a degree sufficient for the end to be attained. 

 If we cannot eat and sins: at -the same moment avc can cat 



