126 



ZOOLOGY. 



Fig. 70. 



and will carry it from the position a b in the direction <f tin- 

 line a c, thus making it traverse, to the point to which 

 it is inserted, a space, which we still represent by 10. Hut 

 if the muscle acts obliquely on the bone, in the dinvtion 



of the line n b, it will then 

 have a tendency to carry it 

 in the direction of b n, and 

 consequently to cause it to 

 approach the articular sur- 

 face r, on which it rests as 

 a point of support. But 

 this being an inflexible body, 

 this displacement cannot 

 take place; the bone can 

 only turn on the point r as 

 on a pivot, and the contrac- 

 tion of the muscle n, without losing any of the energy 

 assigned to it, can only carry the bone in the direction of 

 a d. Three-fourths of its strength will be lost, and it will 

 only be equal to effect a displacement for which one-fourth of 

 the strength expended would have sufficed had its attachment 

 been perpendicular to the bone as the muscle m. 



Now in animal bodies, muscles are generally inserted very 

 obliquely, and thus very unfavourably in respect of their 

 intensity of contraction. The 

 enlargement of the extremities 

 of the bones, as compared with 

 the shafts, serves to counter- 

 balance this obliquity in a cer- 

 tain degree, giving to the joints 

 at the same time more security. 

 The tendons (/) of the muscles ( /// ) 

 situated above the articulations, 

 are inserted generally imme- 

 diately beneath the enlarged extremity of the bone, and thus 

 reach the moveable bone (o) in a direction more approaching 

 the perpendicular, as may readily be understood by comparing 

 figure 72 with 71. 



267. The distance which separates the point of attach- 

 ment of the muscle from the point of support on which the 

 bone moves, and of the opposite extremity of the lever which 

 this organ represents, influences also in the most powerful 

 manner the effects produced by its contraction. 



Fig. 71. 



Fig. 72. 



