530 PHILOSOPHICAL TKANSACTIONS. [aNNO IJQS. 



had taken place ; so that when tiie man recovered, the injured bone, from the 

 position of the fractured parts, was reduced almost one half of its length. By 

 this circumstance, the bicepts flexor cubiti muscle, which bends the fore-arm, 

 remained so much longer than the distance between its origin and insertion, that 

 in the most contracted state it could scarcely bring itself into a straight line ; this 

 muscle however, in time, as the arm recovered strength, adapted itself to the 

 change of circumstances, by becoming as much shorter as the bone was di- 

 minished in length ; and by acquiring a new contraction in this shortened state, 

 it was enabled to bend the fore-arm. Some years after this accident, the person 

 died, and the circumstances above-mentioned being known, the parts were exa- 

 mined with particular attention. The biceps muscles of both arms were carefully 

 dissected out, and being measured, the one was found to be 1 1 inches long, the 

 other only 5 ; so that the muscle of the fractured arm had lost 6 inches, or more 

 than the half of its original length. These muscles are now deposited in Mr. 

 Hunter's collection of preparations illustrating the animal economy. 



Muscular contraction is an operation, in whatever way performed, by which 

 the vital stores of the animal are considerably exhausted ; this is evident from the 

 quantity of blood with which muscles whose action is frequent are supplied. This 

 expence would appear, from observation, to be occasioned rather by the extent 

 of contraction, than by its frequency, or force ; for if we examine the mechanism 

 of an animal body, we shall find a variety of structures evidently intended for no 

 other purpose than diminishing, as much as possible, the necessary extent of 

 contraction in muscular fibres, 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 contraction which is required; and in the muscles of respiration, 

 we find frequency of action is preferred to an increased quantity of muscular con- 

 traction. The velocity of motion thus acquired, though a considerable advan- 

 tage, does not seem to have been thp principal object intended by such structure, 

 but rather to procure the effect by) means of short contractions, which are less 

 fatiguing, or in some other way more in the management of the constitution, 

 than long ones. That long constructions in a muscle cannot be su[)ported for 

 any length of time, may be illustrated from the actions both of the voluntary and 

 involuntary muscles. 



While the voluntary muscles are under the command of the will, we cannot 

 ascertain what would be the effects produced by the continuance of their contrac- 

 tions, since the influence of the brain communicated by the nerve? becomes soon 

 weakened, and puts a stop to their action; but when the contractions of voluntary 

 muscles arc by any circumstance rendered involuntary, the difference in the time 



