Whether the human foot naturally bends to the front, and the hand to the rear.
Further one inquires into the bending of the motive members in animals. And first, whether the human foot naturally bends to the front, and the hand to the rear.
1. It seems not. Four-footed beasts have anterior feet in place of the hands in the human. But beasts bend their anterior feet to the front; therefore, similarly, the human bends the hand to the front.
2. Likewise, bipedal birds are just like the human, but birds bend their feet to the front. Therefore, so too will the human, by the same reasoning.
But the Philosopher says the opposite.
One must say that human feet naturally bend to the front and the hands to the rear, because in every animal the feet extend to that part in which there is more of the body. Now brute beasts extend their rear feet to the front of the body because more of the body is to the front, and the front feet extend and bend to the rear for the same reason, so much so that in the rear feet the knee bends to the rear, but the feet extend toward the front. In the same way, in the front feet the bend is to the front, and the curvature and extension is to the rear. But in the human it is the case that the thigh [coxa] is joined to the trunk [clibanus] and bending occurs to the rear, and for that reason it necessarily extends to the front. The lower leg [crus] is joined to the lower part of the thigh at the knee, and so with respect to the knee the larger part of the body is to the rear, and for that reason it bends to the front and the curvature is to the rear. Nevertheless, the joining of the feet in the human is the opposite. But the human hand is ordered for grasping, and for that reason it naturally curves to the chest. Wings are ordered in the same way in birds, so that the birds move forward using them. For this reason, the curvature in wings is to the front, so that, when extending the extremities of the wings to the front, they come in front of the body, just as sailors when extending the oars reach them out in front of the ship.
Thus, one must respond briefly to the question that the curvature is toward that part toward which or on which there is more of the body.
1. On to the arguments. To the first, one should say that although in quadrupeds the feet are in place of hands in humans, hands work differently from feet and for that reason they bend differently.
2. To the second argument one should say that birds bend their feet to the front because more of the body is on the front, but the wings, contrariwise, bend to the rear. But the human bends the foot to the rear because more of the body is in the rear.
Whether an animal naturally has to place its right foot forward.
It is asked whether an animal naturally has to place its right foot forward.
1. It seems not, because something naturally uses that which suits it when it needs more of that thing. But when a man defends himself, or when he fights, he places his left foot forward. Therefore, he does not naturally place his right foot forward.
2. Likewise, it is not a matter of placing that foot forward on which he supports himself better; but rather he must support himself more on the right foot, since it is stronger, and it is therefore not placed forward.
The Philosopher indicates the opposite.
One should say that every animal properly disposed with respect to its interior organs has naturally to place its right foot forward. And the reason for this is that warmer ones are better fitted for motion. But the heart, which is the principal member, infuses its heat and power more into the right side, and for that reason the right foot is better suited for motion, and the animal places it forward. The left foot, however, is more stable and firmer, just as the Philosopher has it in the second book of the On Heaven and Earth, and for that reason the body supports itself on it more, as is evident among fighters. If it is a male, he places his right foot forward, but, if a female, she places her left foot forward because that part is warmer and rendered better suited for motion. Nevertheless, if there are animals in which the heart inclines greatly to the left, and the liver likewise, these will place the left foot forward.
1. Thus, one should reply to the first argument that when a man is defending himself, he needs to support himself on his foot, and to deflect the blow, and for that reason he sometimes places his left foot forward inasmuch as his right foot is better suited for motion. Thus he does not press his right foot to the earth so much as the left.
2. The answer to the second argument is clear in the same way. For the left foot is much more stable, and for that reason it supports him more, because it moves more slowly, unless affected by some accident.
-  This somewhat cryptic passage is made worse by the fact that for A., coxa can mean "hip" or "thigh." Neither, of course, properly bends. One suspects trouble in the text. Clibanus: lit., "oven." "Now all that lies between the neck and the base of the belly at the groin is called the trunk." DA 22.214.171.124 (SZ 1: 87).