The WALK is a method of progressive motion with a regular individual succession of limb movements. In the evolution of the terrestrial vertebrates the walk was probably the first adopted method of locomotion, and its execution is regulated by the law that the movement of the superior limb precedes the movement of its lateral inferior limb. This is proved not merely by the ordinary quadrupedal walk, but by the suspended motion of the sloth; the crawling of the child upon the ground, the erect walk of man; and the inverse limb movements of the ape tribe.
The relative time intervals of the foot-fallings vary greatly with many species of animals, and even with the same animal under different conditions.
Selecting the horse for the purpose of illustration we find that during the walk—his slowest progressive movement—he has always two, and for a varying period of time, or distance, three feet on the ground at once, while during a very slow walk the support will devolve alternately upon three feet and upon four feet.
If the notation of the foot-fallings commences with the landing of the right hind foot, the order in which the other feet are placed upon the ground will be: the right fore, the left hind, and the left fore, commencing again with the right hind.
Assuming that our observation of the stride of a horse during an ordinary walk commences with the landing of the right hind foot, the body will then be supported by both hind and the left fore feet. The left hind is now lifted, the support of the body devolves upon the diagonals—the right hind and left fore—and continues so supported until the left hind is in the act of passing to the front of the right; when the right fore is next placed on the ground. The left fore is now raised, and the body is supported by the right laterals, until the landing of the left hind foot relieves its fellow hind of a portion of its weight. Two steps or one-half of a stride have now been made, and with the substitution of the right feet for the left, two other steps will be executed in practically the same manner, and a full stride will have been completed. We thus see that during the walk a quadruped is supported by eight different methods, the supporting limbs being consecutively:
Both hind and left fore.
Right hind and left fore diagonals.
Right hind and both fore.
Right hind and right fore laterals.