The foot quits the ground ([Fig. 120], C); this may be called lifting; the limb is oblique in direction downwards and backwards. This same limb is flexed and carried forward ([Fig. 120], B), and, as it is supported by the action of its flexors, this is the period named suspension; the hoof is vertical. Then the limb is carried still further forward, becoming extended ([Fig. 120], A); the heel is lowered, and the foot, being oblique, is directed towards the ground; this is the placing.
Fig. 121.—Swing of the Anterior Limb on the Point of Pressure (after G. Colin).
A, Commencement of the pressure; B, centre of the pressure; C, termination of the pressure.
Then takes place pressure ([Fig. 121]). The foot has just been placed on the ground; the limb is oblique in direction downwards and forwards; this we call commencement of the pressure ([Fig. 121], A). Then the body, being carried forward, whilst the hoof, D, is fixed on the ground, the limb becomes vertical: this stage is mid-pressure ([Fig. 121], B). Finally, the progression of the body continuing, the limb becomes oblique downwards and backwards; it is now at the termination of pressure ([Fig. 121], C), and proceeds to lift itself anew if another step is to be made.
In conclusion, the inferior extremity of the limb describes, from its elevation to its being placed on the ground, an arc of a circle around its superior extremity ([Fig. 121], D); whilst, during the pressure, it is its superior extremity which describes one around its inferior extremity, then fixed on the ground ([Fig. 121], D).
If we simultaneously examine the two fore-limbs, we remark that when one of them begins its pressure the other ends it, and vice versâ.
