104 THE MECHANICAL FUNCTIONS. 



ly the structure is rendered still more complex, by the in- 

 terposition of several tendinous layers among the fleshy 

 fibres. This arrangement, which constitutes a complex tuus- 

 cle, (as shown in Fig. 42) occurs, for example, in the Soiasus, 

 or large muscle, which raises the heel, and forms the thick- 

 est part of the calf of the leg. 



It very commonly happens in the animal frame, as it 

 does in other machines, that the presence of the moving 

 agent in the spot where its action is w^anted, would be ex- 

 ceedingly inconvenient. The usual plan adopted for trans- 

 ferring 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 performed its office as a delicate mechani- 

 cal instrument. 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 

 farther advantage, that by their intervention the united pow- 

 er of all the fibres of the muscle may be obtained, and con- 

 centrated upon any particular point. In this respect, like- 

 wise, they resemble 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 principal use of ten- 

 dons 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 trans- 

 mission, and producing the effect of pulleys. 



In a great number of muscles, the fibres, instead of running- 

 parallel to one another, are made either to converge, or to 

 diverge, in order to suit particular kinds of movements: and 



