124 I'Hi: MECHANICAL FUNCTIONS. 



soheus, or large muscle, which raises the heel, and 

 forms the thickest part of the calf of the leg. 



It very commonly happens in the animal i'rame, 

 as it does in other machines, that the presence of 

 the moving agent in the place where its action is 

 wanted, would be exceedingly inconvenient. The 

 usual plan adopted for transferring the effect of the 

 moving power to a distant point is the employment 

 of a rope, or strap. Such is precisely the office of 

 the tendons, which are long straps, attached at one 

 end to the muscle, and at the other to the bone, or 

 other part intended to be moved. (See Fig. 43). 

 If the hand, for instance, had been encumbered 

 with all the muscles which are necessary for the 

 movements of the fingers, it never could have per- 

 formed its office as a delicate mechanical instru- 

 ment. These muscles, accordingly, are disposed 

 high up on the arm, and their tendons are made to 

 pass along the wrist to the joints of the fingers 

 which are to be moved. 



The employment of tendons is accompanied with 

 this further advantage, that by their intervention 

 the united power of all the fibres of the muscle 

 may be obtained, and concentrated upon any par- 

 ticular point. In this respect, likewise, they re- 

 semble a rope, at which a great number of men are 

 pulling at the same moment, and whose combined 

 strength is thus brought into action. Another prin- 

 cipal use of tendons is that a different direction 

 may, by their means, be given to the moving power, 

 without altering its position. Many instances occur 

 of their application in this manner, by their being 

 made to pass round corners of bones, and along 

 grooves or channels, expressly formed for their 

 transmission, and producing the effect of piillies. 



