INTRODUCTION. 



21 



In this outline of the theory of the lever, the forces have 

 been considered as acting vertically, or parallel to the direc- 

 tion of the force of gravity. 



Passive Organs of Locomotion. Bones. — The solid frame- 

 work or skeleton of animals which supports and protects their 

 more delicate tissues, whether chemically composed of ento- 

 moline, carbonate, or phosphate of lime ; whether placed in- 

 ternally or externally ; or whatever may be its form or 

 dimensions, presents levers and fulcra for the action of the 

 muscular system, in all animals furnished with earthy solids 

 for their support, and possessing locomotive power." ^ The 

 levers and fulcra are well seen in the extremities of the deer, 

 the skeleton of which is selected for its extreme elegance. 



Fig. 4. Skeleton of the Deer (after Pander and D'Alton). The bones in the ex- 

 tremities of this the fleetest of quadrupeds are inclined very obliquely towards 

 each other, and towards the scapular and iliac bones. This arrangement in- 

 creases the leverage of the muscular system and confers great rapidity on 

 the moving parts. It augments elasticity, diminishes shock, and indirectly 

 begets continuity of movement, a. Angle formed by the femur with the 

 ilium, h. Angle formed by the tibia and flbula with the femur, c. Angle 

 formed by the cannon bone with the tibia and fibula, d. Angle formed by 

 the phalanges with the cannon bone. e. Angle formed by the humerus with 

 the scapula. /. Angle formed by the radius and ulna with the humerus. 



1 Bishop, ojp. cit. 



