NOTES AND ADDITIONS. 



297 



Hues which are to represent positive tension are drawn 

 upward, those which are to represent negative tension down- 

 ward, from the basal line. The figure then shows that 

 the tension in the middle of the wire = 0, and that toward 

 the left the positive, toward the right the negative, tensions 

 increase regularly. In order to find the amount of the 

 tension, prevailing at any particular point, e.g. at e, a per- 

 pendicular line is erected at that point; and the length 

 of this, e f, accurately represents the tension there pre- 

 vailing. 



2. DIRECTION OF THE MUSCLE-FIBRES, HEIGHT OF ELEVATION, 

 AND THE ACCOMPLISHMENT OF WORK (p. 93). 



Because of the extreme rarity of long parallel-fibred 

 muscles, it is interesting to examine more closely the in- 

 fluence which oblique arrangement of the 

 fibres exercises on their force, height of ele- 

 vation, and on the work which they accom- 

 plish. When a muscle-fibre is so arranged 

 that it is incapable of effecting a movement 

 in the direction of its own contraction, only a 

 part of the force of tension which is generated 

 in it by its contraction comes into play, and 

 this part may be easily found by the law of 

 the parallelogram of forces. This is the case 

 in all simply and doubly penniform muscles. 

 Supposing that the muscle-fibre A B (fig. 71) 

 contracts to the extent B b, but that motion 

 of the point , on account of the attachment 

 of the muscle to the bone, and of the nature 

 of the sockets of the latter, can only occur in 

 the direction B C ; in that case the muscle- 

 fibre, in contracting, undergoes a change in 

 direction from its fixed point of origin A, and thus assumes 

 the position A b' ; the elevation which is really effected is, 

 14 



B 



IMG. 71. ACTION 



OFOBtlQUEML'S- 

 CLE-FIBKES. 



