Abstract
The earliest movements of the hind leg are adduction and abduction, and they occur only with action of the trunk. At about the same time that this type of movement appears, or probably a little later, the hind leg elevates when the animal is rotated dorsally on its longitudinal axis on the side of the reacting limb. This movement of the hind leg is co-ordinated with elevation of the fore limb. This integrated action of fore and hind limbs with action of the trunk is a typical postural reaction and it occurs before a local reflex of the hind leg can be excited. Before local exteroceptive reflexes of the hind leg appear there occur also strong simultaneous abduction of both hind legs in coordination with elevation of the head and fore part of the trunk; the typical walking posture, i. e., flexure of the trunk with the adduction of the fore legs and abduction of the hind leg on the concave side while on the opposite side the fore leg is abducted and the hind leg adducted; and, at least in many cases, typical walking.
Tactile stimulation of the leg excites action of the animal as a whole until just before local reflexes of the leg appear, when such stimulation inhibits all body movement. Local reflexes of the hind leg in response to exteroceptive stimulation on the leg and on the skin of the trunk behind and near the leg make their appearance at about the same time. These reflexes begin at about the same time that antigravity action of the legs can first be detected. This is before there is rotation of the leg or passive bending of the knee under antigravity pressure.
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