PHYSIOLOGY OF MOVEMENT. 751 



the ground and gives the forward impetus to the body ; the right hind 

 leg and left foreleg are swinging forward, while the flexed right fore leg 

 is being advanced. 2. The right hind foot and left fore foot then strike 

 the ground and receive the weight of the body ; the left hind leg is 

 extended behind the body and about to leave the ground, while the fully 

 extended right fore leg is advanced. 3. Then the right fore leg reaches 

 the ground and sustains the weight of the body until the limb is vertical ; 

 the left hind leg leaves the ground, and the flexed right hind leg and left 

 lore leg are swinging forward. Finally, the right fore foot leaves the 

 ground, the leg being strongly flexed, and the body moves through the 

 air from the impetus from the left, aided by the right, hind leg. The 

 three strokes of the hoof correspond to the three actions described 

 above as 1, 2, and 3. The pause between the first and second sounds is 

 short, that between the second and third still shorter, while between the 

 third and first, and while the body is moving through the air, the pause 

 is considerably longer. 



In this gait, as in the run and long jump, and occasionally in the 

 high jump, the weight of the body when.it first reaches the ground is 

 not received on the fore legs, but through rapid flexion the hind legs 

 first touch the ground. 



In the canter the action of all the limbs is much slower, the verte- 

 bral column being more raised, the gait, therefore, more resembling the 

 high than the long jump. The fall of the diagonal feet is separated by a 

 short interval; so in the canter four strokes of the hoofs are heard. 



The plates following page 921, through the kind permission of Pro- 

 vost Pepper, of the University of Pennsylvania, and Mr. Muybridge, are 

 reproduced from the elaborate series of instantaneous photographs made 

 by Mr, Muybridge in the University of Pennsylvania. 



5. Other Movements in the Horse. — (a) Rearing— In the act of rear- 

 ing the fore part of the body becomes raised up on the hind extremities, 

 so that the vertebral column leaves the horizontal direction and becomes 

 nearly vertical. The first stage of rearing consists in the fixation of the 

 hind legs, the elevation of the neck and head, and the contraction of the 

 back and lumbar muscles, by which the vertebral column becomes rigid ; 

 then the elevation of the fore legs commences with a slight bowing of 

 the extremities and subsequent powerful extension, by which the feet are 

 raised up from the ground and become flexed. Then there is a powerful 

 contraction of the back muscles (the ilio-spinal, the gluteal muscles, and 

 the ischio-tibial muscles), the anterior extremity of the vertebral column 

 is somewhat raised up, its elevation being assisted by the drawing down 

 of the pelvis by means of the lumbar muscles, so that the weight of the 

 body is now borne by the flexed hind legs (Fig. 310). The vertebral 

 column ordinarily does not quite reach the vertical line, but yet the line of 



