424 GENERAL ANATOMY. 



is applied to the orifice of the auricular canal, as well as that 

 which is perceived by the application of the stethoscope on 

 the muscle in action. This phenomenon is principally and 

 perhaps solely rendered appreciable in a muscle where the 

 action is ke'pt up for some time. It has only been observed 

 to exist, either by the help of the sight or hearing, in the exte- 

 rior muscles, and in the heart. 



676. Certain muscles are capable of partial contraction. 

 This is at least seen in the experiments on living animals, and 

 in some cases of convulsion of the subcutaneous muscles. Is 

 this peculiar to the muscles which have several nerves? 



677. The rapidity as well as the force of contraction 

 are extremely great; the rapidity is very great in the action 

 of running, in that of speaking fastj in that of playing on 

 stringed instruments, &c. This rapidity, in some cases, may 

 be carried to less than a third in point of time. The force of 

 the muscles when in action is enormous, and is sometimes 

 sufficient to rupture the tendons -or the bones, parts of the 

 body so capable of resisting rupture; it is always in propor- 

 tion to the number of muscular fibres, each of which possesses 

 its own force, which is a fraction of the total force. The elas- 

 ticity of the contracted muscles is particularly manifest in the 

 production of the voice. 



678. It is difficult to determine the extent .of the contrac- 

 tion; it has been attempted on the principle of certain hypo- 

 thetical ideas as to the form of the primitive fibres, and it has 

 thus been estimated at one third the length of the fibre. Direct 

 observation demonstrates that Jhe shortening of the contracted 

 fibre, in the exterior muscles, is the fourth of its length; Messrs. 

 Prevost and Dumas have arrived at the same result by mea- 

 suring the angles, which are formed during.co.ntraction. How- 

 ever this may be, the extent of the contraction is always in 

 proportion to the length of the muscular fibres. When nothing 

 is opposed to the contraction of the muscle, it is capable of 

 producing a very great .shortening, examples of which are 

 seen in cases of fracture, and loss of substance in the bones 

 and members. 



679. The conditions of muscular action are the life of the 



