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PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



astragalo-tibial articulation to the ground, and the resistance is the weight 

 of the body. This mode of action of the gastrocnemius is more evident 

 in man (Pig. 297) when the weight of the body is raised on the toes 

 through the action of this muscle. In the anterior extremity of quad- 

 rupeds the extensors of the forearm (A D, B D, and CD, Fig. 292) also 

 act through levers of the second class when the foot is on the ground, 



Fie. 295.— The Anterior Extremity 

 of the Horse in Flexion. (Colin.) 



A B, line of action of infraspinatus. CD, line 

 of action of biceps flexor. E F, line of action of 

 metacarpal flexor. G H, line of action of flexor 

 pedis. 



Fig. 296.— Posterior Extremity of 

 the Horse in Flexion. {Colin.) 



A B. line of action of superficial gluteus 

 muscle. C D, line of action of ischio-tibial 

 muscles. E F, line of action of metatarsal 

 flexor. 6? U, lines of action of flexors of foot. 



their action serving then to flex the humero-radial articulation, instead 

 of extending it, as occurs when they act with the foot in the air. 



The movements of the different parts of the animal body depend 

 upon the union of the different parts of the skeleton with each other and 

 the mode of insertion of the muscles. The movable parts of the skeleton 

 are designated as joints, the relative positions of the bones forming a 



