Artistic Anatomy of Animals Part 37

[Ill.u.s.tration: FIG. 124.--THE AMBLE: RIGHT LATERAL PRESSURE.[72]]

[72] The figures which, in the present study, reproduce the different paces, have been made from our articulated horse (see the note on p. 282).

=The Amble.=--To give an exact idea of the general character of the amble, let us fancy the two men whom we discussed above marching one behind the other and walking in step--that is, moving the legs of the same side simultaneously. They will thus represent the amble, which, indeed, results from the alternate displacements of the lateral bipeds; the limbs of the same side (right or left) execute the same movements in the same time.

This is what the notation indicates (Fig. 123). We there see that the pressures of the right fore-foot, marked by the white bands in the upper range, are exactly superposed on those of the right hind one, which are marked by a similar band on the lower line; this means that the pressures took place in the same time. We there see also a similar arrangement of the gray bands, which has a similar significance for the left fore and hind feet.

And if we recollect the three phases of pressure (see p. 289, and Figs.

121, 122), we shall comprehend, in looking at the diagrams, that, at the initial stage (A), the limbs are commencing their pressure, and are oblique downwards and forwards; that afterwards (B) the two limbs are vertical, since they are at the middle of the pressure stage; and that finally (C) they are oblique downwards and backwards, for it is then the termination of their pressure (Fig. 124).

[Ill.u.s.tration: FIG. 125.--NOTATION OF THE GAIT OF THE TROT IN THE HORSE (AFTER PROFESSOR MAREY).]

During the time that the right limbs are pressing (notation, white bands) the left limbs are raised; afterwards these latter take up the pressure (gray bands), and then the right limbs are raised in their turn.

During the pace of ambling the weight of the body, which is wholly sustained by the limbs of one side only, is not in equilibrium, so that the limbs which are raised return by a brisk movement to the position of support in order to re-establish it.

=The Trot.=--We have just seen that, in order to represent the amble, the two marchers moved their right limbs simultaneously, and then their left ones.

Let us suppose now that the hinder man antic.i.p.ated by half a pace the movement of the front one, then will be found realized the a.s.sociation and the nature of the displacements of the limbs during the pace of the trot.

By this antic.i.p.ation of a half-step (we have defined, p. 288, what is to be understood by the word _step_), it follows that when the marcher who is in front advances his right leg it is the left leg of the marcher who follows him that is carried in the same direction. We should thus conclude from this that the trot is characterized by a succession of displacements of the diagonal bipeds.

[Ill.u.s.tration: FIG. 126.--THE TROT; RIGHT DIAGONAL PRESSURE.]

[Ill.u.s.tration: FIG. 127.--THE TROT; TIME OF SUSPENSION.]

Indeed, if we examine the notation of this gait (Fig. 125), we see that with the pressure of the right fore-foot is found a.s.sociated the pressure of the left hind-foot. It is, accordingly, a typical diagonal biped (Fig. 126).

[Ill.u.s.tration: FIG. 128.--NOTATION OF THE PACE OF STEPPING IN THE HORSE (AFTER PROFESSOR MAREY).

L, Right lateral pressure; D, right diagonal pressure; L', left lateral pressure; D', left diagonal pressure.]

But it is necessary to add that these groups of pressures do not succeed one another without interruption, except in the slow trot. In the ordinary trot, or in that in which the animal's strides are very long, the body between each of the double pressures which we have just been considering is projected forward with such force that it remains for an instant separated from the ground. This is what we designate by the name of _time of suspension_ (Fig. 127). The notation in this case would be slightly different from that which we reproduce above, in this sense: that between the diagonal pressures there then would be found an interval, since during the time the body is suspended none of the feet can produce a pressure-mark (see, with regard to these intervals, the notations of the running of a man, Fig. 118, and Fig. 119, 3, 4).

=The Walk.=--Although slow, a feature which would seem to make it possible to permit its a.n.a.lysis in a horse when walking, this pace is difficult to comprehend without sufficient preliminary study.

[Ill.u.s.tration: FIG. 129.--THE STEP: RIGHT LATERAL PRESSURE.]

[Ill.u.s.tration: FIG. 130.--THE STEP: RIGHT DIAGONAL PRESSURE.]

We saw above that in order to represent the amble the marchers had to move the legs of the same side simultaneously. We have also just seen that in order to represent the trot the marcher at the back had to antic.i.p.ate by a half-step. Suppose, now, that this same marcher antic.i.p.ates the man in front by a quarter-step only, or by a half-pressure period, and thus will be found realized the order of succession of the limbs in the gait or pace called the _walk_. The feet meet the ground one after the other, since they are each in advance by half the duration of a pressure. The strokes are four in number during the period of a step of this pace; in the amble and in the trot they do not exceed two, for then the limbs strike the ground in lateral diagonal pairs.

[Ill.u.s.tration: FIG. 131.--THE GALLOP: FIRST PERIOD.]

[Ill.u.s.tration: FIG. 132.--THE GALLOP: SECOND PERIOD.]

[Ill.u.s.tration: FIG. 133.--THE GALLOP: THIRD PERIOD.]

[Ill.u.s.tration: FIG. 134.--THE GALLOP: TIME OF SUSPENSION.]

If we examine the notation of the pace of walking (Fig. 128), we see that the right fore-foot commences its pressure when the right hind-foot is in the middle of its own, and that the hinder left begins in the middle of that of the right fore-foot, and that it is itself at the midst of its pressure when the left fore-foot touches the ground, etc. In a word, the foot-fallings occur in the following order and at regular intervals--the fore right foot is here considered as acting first: right fore, left hind, left fore, right hind, and so on in succession.

[Ill.u.s.tration: FIG. 135.--NOTATION OF THE GALLOP DIVIDED INTO THREE PERIODS OF TIME (AFTER PROFESSOR MAREY).

1, First period; 2, second period; 3, third period.]

As to the nature of the bipeds which succeed one another, it is easy to understand them by means of the notation. In reading this from left to right, we see that the a.s.sociations of pressure are first made by the two right feet, then by a right foot and a left one, then by two left feet, and, finally, by a left and right. It is, accordingly, a succession this time of lateral and diagonal pressures.

[Ill.u.s.tration: FIG. 136.--NOTATION OF THE GALLOP OF FOUR PERIODS IN THE HORSE (AFTER PROFESSOR MAREY).

1, First period; 2, second period; 3, third period; 4, fourth period.]

Thus, we find at the start a right lateral pressure (Fig. 129), next a right diagonal (Fig. 130), then a left lateral; finally, a left diagonal pressure. It is thus that the initial letters L, D, L', D' further indicate the notations represented in Fig. 128.

=The Gallop.=--The ordinary gallop is a pace of three phases. The first is characterized by the fact that one hind-limb alone rests on the ground (Fig. 131); in the second the animal is on a diagonal support (Fig. 132); in the third it comes down on a fore-limb (Fig. 133). The body is then raised (Fig. 134), and to this period of suspension succeed anew the three modes of pressure indicated above.

The gallop is said to be from either right or left. In the gallop from the right, the right fore-leg is the more frequently in advance of its neighbour; it is the last to be placed on the ground. The left foot of the posterior biped is the one which commences the action.

An entirely opposite arrangement characterizes the gallop from the left.

[Ill.u.s.tration: FIG. 137.--LEAP OF THE HARE (AFTER G. COLIN).]

The notation reproduced in Fig. 135 corresponds to the gallop from the right. It is there seen, as we pointed out above, that in the first phase the exclusive support of the left hind-foot takes place (1); that afterwards, in the second, commence simultaneously, the pressures of the left fore and the right hind foot (2); this is the left diagonal support; and that finally, in the third, the body comes down on a fore-limb, which is then the right (3); and that for a moment it is on this limb alone that the animal rests.

To these three phases on the notation succeeds an interval; this is the period of suspension.

The gallop of four phases only differs from the preceding in that the foot-fallings of each diagonal biped occur at slight intervals, and give distinct sounds. The notation is reproduced in Fig. 136.

[Ill.u.s.tration: FIG. 138.--THE LEAP.]

[Ill.u.s.tration: FIG. 139.--THE LEAP.]

[Ill.u.s.tration: FIG. 140.--THE LEAP.]

[Ill.u.s.tration: FIG. 141.--THE LEAP.]

=The Leap.=--The leap is an act by which the body is wholly raised from the ground and projected upwards and forwards to a greater or less distance.

It is prepared for by the flexing of the hind-limbs, which, by being suddenly extended, project the body, and thus enable it to pa.s.s over an obstacle.

This preparatory arrangement is very remarkable in the leap of the lion, the cat, and the panther, which execute springs of great length; in the horse, in which the leap is not an habitual mode of progression, this flexion of the hinder limbs is less marked. With this animal the leap is generally a.s.sociated with the gallop; nevertheless, it is sometimes made from a stationary position. In observing the hare or the rabbit, in which the leap is habitual, we notice (Fig. 137) that the hind-limbs, being extremely flexed, rest on the ground as far as the calcaneum, are then straightened by the action of their extensors, become vertical and then oblique backwards at the moment the body is thrown forward into s.p.a.ce by the sudden extension of these limbs.

The action of the extensors is energetic and instantaneous, and their energy is greater than in ordinary progression, for it is required to lift the body and to project it forcibly a more or less considerable distance. It is the extreme rapidity of this action which enables the animal to clear an obstacle, for without this condition the body would be raised, but not separated from the ground.

First of all, in reaching the obstacle to be cleared, the horse prepares to leap by taking the att.i.tude of rearing; the hind-limbs are flexed and carried under the body, the fore-quarters are raised, and the different segments of the fore-limbs are flexed (Fig. 138).

[Ill.u.s.tration: FIG. 142.--THE LEAP.]