82 
OF THE MUSCLES. 
the mechanical, and for preventing one set of actions in 
terfering with the other. Where various functions are 
united, the difficulty is to guard against the inconve¬ 
niences of a too great complexity. In no apparatus put 
together by art, and for the purposes of art, do I know such 
multifarious uses so aptly combined, as in the natural or¬ 
ganization 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 single cavity; is one machine; 
with its parts neither crowded nor confused, and each un¬ 
embarrassed by the rest: each at least at liberty in a de¬ 
gree sufficient for the end to be attained. If we cannot 
eat and sing at the same moment, we can eat one moment, 
and sing the next: the respiration proceeding freely all the 
while. 
There is one case, however, of this double office, and 
that of the earliest necessity, which the mouth alone could 
not perform; and that is, carrying on together the two ac¬ 
tions of sucking and breathing. Another route, therefore, 
is opened for the air, namely, through the nose, which lets 
the breath pass backward and forward, whilst the lips, in the 
act of sucking, are necessarily shut close upon the body 
from which the nutriment is drawn. This is a circum¬ 
stance which always appeared to me worthy of notice. 
The nose would have been necessary, although it had not 
been the organ of smelling. The making it the seat of a 
sense, was superadding a new use to a part already wanted; 
was taking a wise advantage of an antecedent and a con¬ 
stitutional necessity. 
But to return to that which is the proper subject of the 
present section—the celerity and precision of muscular mo¬ 
tion. These qualities may be particularly observed in the 
execution of many pieces of instrumental music, in which 
the changes produced by the hand of the musician are ex¬ 
ceedingly rapid; are exactly measured, even when most 
minute; and display, on the part of the muscles, an obedi¬ 
ence of action, alike wonderful for its quickness and its 
correctness. 
Or let a person only observe his own hand whilst he is 
writing ; the number of muscles which are brought to 
bear upon the pen: how the joint and adjusted operation 
of several tendons is concerned in every stroke, yet that 
five hundred such strokes are drawn in a minute. Not a 
letter can be turned without more than one, or two, or three 
tendinous retractions, definite, both as to the choice of 
