OF TIIE MUSCLES. 
83 
the tendon, and as to the space through which the re¬ 
traction moves; yet how currently does the work proceed! 
and when we look at it, how faithful have the muscles 
been to their duty, how true.to the order which endeavour 
or habit hath inculcated! For let it be remembered, that 
whilst a man’s hand-writing is the same, an exactitude of 
order is preserved, whether he write well or ill These 
two instances, of music and writing, show not only the 
quickness and precision of muscular action, but the do¬ 
cility. 
II. Regarding the particular configuration of muscles, 
sphincter or circular muscles appear to me admirable pieces 
of mechanism. [PI. XIV. fig. 3.] It is the muscular pow¬ 
er most happily applied; the same quality of the muscular 
substance, but under a new modification. The circular 
disposition of the fibres is strictly mechanical; but, though 
the most mechanical, is not the only thing in sphincters 
which deserves our notice. The regulated degree of con¬ 
tractile force with which they are endowed, sufficient for 
retention, yet vincible when requisite; together with their 
ordinary state of actual contraction, by means of which 
their dependence upon the will is not constant, but occasion¬ 
al, gives to them a constitution, of which the conveniency 
is inestimable. This their semi-voluntary character, is ex¬ 
actly such as suits with the wants and functions of the ani¬ 
mal. 
III. We may also, upon the subject of muscles, observe, 
that many of our most important actions are achieved by 
the combined help of different muscles. Frequently, a 
diagonal motion is produced by the retraction of tendons 
pulling in the direction of the sides of the parallelogram. 
This is the case, as hath been already noticed, with some 
of the oblique nutations of the head. Sometimes the num¬ 
ber of co-operating muscles is very great. Dr. Nieuentytj 
in the Leipsic Transactions, reckons up a hundred muscles 
that are employed every time we breathe; yet we take in, 
or let out, our breath, without reflecting what a work is 
thereby performed; what an apparatus is laid in, of instru¬ 
ments for the service, and how many such contribute their 
assistance to the effect! Breathing with ease, is a blessing 
of every moment; yet, of all others, it is that which we 
possess with the least consciousness. A man in an asthma 
is the only man who knows how to estimate it. 
IV. Sir Everard Home has observed,* that the most 
important and the most delicate actions are performed in the 
* Phil. Trans, part 1 . 1800. p. 8. 
