on Muscular Motion. s'l 1 
mined with particular attention. The biceps muscles of both 
arms were carefully dissected out, and being measured, the 
one was found to be eleven inches long, the other only five ; 
so that the . muscle of the fractured arm had lost six inches, 
which is more than the half of its original length. These 
muscles are now deposited in Mr. Hunter's collection of pre- 
parations illustrating the animal oeconomy. 
That -muscles possessed this power, has been- taken notice 
of by Mr. Hunter in a former lecture ; but the instance which 
I have given, is so striking an illustration of this principle, 
that I could not avoid mentioning it while upon this subject. 
Muscular contraction is an operation, in whatever way per- 
formed, by which the vital stores of the animal are conside- 
rably exhausted ; tlTis is evident from the quantity of blood 
with which muscles whose action is frequent are supplied. 
This expence would appear, from observation, to be occa- 
sioned rather by the extent of contraction, than by its fre- 
quency, or force ; for if we examine the mechanism of an 
animal body, we shall find a variety of structures evidently 
intended for no ether purpose than diminishing, as much as 
possible, the necessary extent of contraction in muscular fi- 
bres, while there is no such prevention of frequency of action. 
Muscles in general are applied to the bones in such way as 
to act with great mechanical disadvantages as to power ; but 
this is more than compensated by the small quantity of con- 
traction which is required ; and in the muscles of respiration, 
we find frequency of action is preferred to an increased quan- 
tity of muscular contraction. 
The velocity of motion thus acquired, although a consi- 
derable advantage, does not seem to have been the principal 
E e 2 
