nil-: iioKsr. IN MOTION. 113 



propelling power in the direction of the centre of gravity, as in Un- 

 bound of the deer and the leap of the horse ; for if it were given 

 above it the animal would be pitched headlong. The hind foot should 

 be the last to leave the ground on a priori reasoning ; and on consulting 

 the silhouettes of the trotting horse (Plates XXXVI. -XL.), such will 

 h found to be the fact. The early start of the fore foot enables it to 

 clear the way for the hind one on the same side to advance to the 

 support of the centre of gravity in its turn without being hit by it, or 

 overreached, as it is technically called. In the mean time the fore 

 foot, having a more circuitous route to travel, is enabled to attain its 

 position as a supporter at the same instant as its co-operating 

 partner. 



The position in which the feet fall is as nearly on a line as is possi- 

 ble without their interference, both in the trot and run, as may be 

 seen by referring to the illustrations of the paces in the latter part 

 of this volume, where the animals are seen in various aspects of the 

 same position. 



Interference with the posterior feet is rendered very difficult by the 

 mechanical arrangement of the hock joint, already explained, which 

 causes an involuntary circumduction of the hind feet as they pass each 

 other, and yet compels the feet to be planted successively near the 

 same base line. In the case of the anterior extremities there is no 

 corresponding contrivance, but the breadth of the shoulders renders it 

 unnecessary. 



For obvious reasons it is not possible to show by the camera the 

 occurrence of interference, but overreaching is shown in Plate XXXVI. 

 Figs. 2, 10, and in Plate XXXIX. Fig. 9. The fore foot being dila- 

 tory, or the disproportion in the length of the body to that of the legs, 

 exposes the fetlock and heel to injury from the shoe of the hind foot ; 

 but generally the hind foot is pushed under the forward one as the 

 latter rises. 



There is a pace closely allied to the trot, and differing from it 

 only in one particular, and that is that the limbs do not move diago- 

 nally in pairs, but those on the same side move together. This pace is 

 shown in Plate XLIX. Comparing this series with a trotting series 



