§1313 Ὄντων δὲ τεττάρων τρόπων τῆς κάμψεως κατὰ τοὺς συνδέσμους (ἀνάγκη γὰρ κάμπτειν ἢ ἐπὶ τὸ κοῖλον καὶ τὰ πρόσθια καὶ τὰ ὀπίσθια, καθάπερ ἐφʼ οἷς Α, ἢ ἐπὶ τοὐναντίον ἐπὶ τὸ κυρτόν, καθάπερ ἐφʼ οἷς Β, ἢ ἀντεστραμμένως μὴ ἐπὶ τὰ αὐτά, ἀλλὰ τὰ μὲν πρόσθια ἐπὶ τὸ κυρτόν, τὰ δʼ ὀπίσθια ἐπὶ τὸ κοῖλον, καθάπερ ἐφʼ οἷς τὸ Γ ἢ τοὐναντίον τούτοις τὰ μὲν κυρτὰ πρὸς ἄλληλα, τὰ δὲ κοῖλα ἐκτός, καθάπερ ἔχει ἐφʼ οἷς τὸ ∠), ὡς μὲν ἔχει ἐφʼ οἷς τὸ Α ἢ τὸ Β, οὐθὲν κάμπτεται οὔτε τῶν διπόδων οὔτε τῶν τετραπόδων, ὡς δὲ τὸ τὰ τετράποδα, ὡς δὲ τὸ ∠, τῶν μὲν τετραπόδων οὐθὲν πλὴν ἐλέφας, ὁ δʼ ἄνθρωπος τοὺς βραχίονας καὶ τὰ σκέλη· τοὺς μὲν γὰρ ἐπὶ τὸ κοῖλον κάμπτει, τὰ δὲ σκέλη ἐπὶ τὸ κυρτόν.
13 There being four ways of bending at the joints, (for it is necessary to bend either towards the concave both the front and the hind legs, as in the case of those with A, or on the contrary towards the convex, as in the case of those with B, or alternately not towards the same parts, but the front legs towards the convex and the hind legs towards the concave, as in the case of those with Gamma, or in the contrary way to these, with the convex parts towards one another and the concave parts on the outside, as is the case with those with Angle [∠]), as is the case with those with A or B, nothing bends, neither of bipeds nor of quadrupeds, but as Gamma, the quadrupeds bend, and as Angle, of quadrupeds nothing bends except the elephant, but man bends his arms and his legs; for he bends the former towards the concave, and his legs towards the convex.
ἀεὶ δʼ ἐναλλὰξ ἐναντίως ἔχει τὰ κῶλα τὰς κάμψεις τοῖς ἀνθρώποις, οἷον τὸ ὠλέκρανον ἐπὶ τὸ κοῖλον, ὁ δὲ καρπὸς ἐπὶ τὸ κυρτόν, καὶ πάλιν ὁ ὦμος ἐπὶ τὸ κυρτόν· ὡσαύτως δὲ καὶ ἐπὶ τῶν σκελῶν ὁ μηρὸς ἐπὶ τὸ κοῖλον, τὸ δὲ γόνυ ἐπὶ τὸ κυρτόν, ὁ δὲ ποὺς τοὐναντίον ἐπὶ τὸ κοῖλον.
And the limbs always have their bendings alternately in opposite directions for humans, for instance the elbow towards the concave, but the wrist towards the convex, and again the shoulder towards the convex; and likewise also in the case of the legs, the thigh towards the concave, but the knee towards the convex, and the foot on the contrary towards the concave.
καὶ τὰ κάτω δὴ πρὸς τὰ ἄνω φανερὸν ὅτι ἐναντίως· ἡ γὰρ ἀρχὴ ὑπεναντίως, ὁ μὲν ὦμος ἐπὶ τὸ κυρτόν, ὁ δὲ μηρὸς ἐπὶ τὸ κοῖλον· διὸ καὶ ὁ μὲν ποὺς ἐπὶ τὸ κοῖλον, ὁ δὲ καρπὸς τῆς χειρὸς ἐπὶ τὸ κυρτόν.
And indeed, it is clear that the lower parts are opposite to the upper parts; for their beginning is contrary, namely, the shoulder towards the convex, but the thigh towards the concave; wherefore also the foot is towards the concave, and the wrist of the hand towards the convex.
§14Αἱ μὲν οὖν κάμψεις τῶν σκελῶν τοῦτόν τε τὸν τρόπον ἔχουσι καὶ διὰ τὰς αἰτίας τὰς εἰρημένας, κινεῖται δὲ τὰ 14 ὀπίσθια πρὸς τὰ ἔμπροσθεν κατὰ διάμετρον· μετὰ γὰρ τὸ δεξιὸν τῶν ἔμπροσθεν τὸ ἀριστερὸν τῶν ὄπισθεν κινοῦσιν, εἶτα τὸ ἀριστερὸν τῶν ἔμπροσθεν, μετὰ δὲ τοῦτο τὸ δεξιὸν τῶν ὄπισθεν.
The bendings of the legs, then, are in this manner and for the reasons mentioned, but the hind legs move in relation to the front legs diagonally; for after the right of the front legs they move the left of the hind legs, then the left of the front legs, and after this the right of the hind legs.
αἴτιον δʼ ὅτι εἰ μὲν τὰ ἔμπροσθεν ἅμα καὶ πρῶτον, διέσπαστο ἂν ἢ καὶ προπετὴς ἂν ἐγίνετο ἡ βάδισις καὶ οἷον ἐφελκομένοις τοῖς ὄπισθεν.
And the cause is that if the front legs moved together and first, the walking would be torn asunder or would become headlong, with the hind legs being as it were dragged behind.
ἔτι δʼ οὐ πορεία ἀλλὰ ἅλσις τὸ τοιοῦτον· χαλεπὸν δὲ συνεχῆ ποιεῖσθαι τὴν μεταβολὴω ἁλλόμενα.
Furthermore, such a movement is not walking but jumping; and it is difficult to make the movement continuous while jumping.
σημεῖον δέ· ταχὺ γὰρ ἀπαγορεύουσι καὶ νῦν τῶν ἵππων ὅσοι τὸν τρόπον τοῦτον ποιοῦνται τὴν κίνησιν, οἷον οἱ πομπεύοντες.
And here is a sign: for those of horses that perform their movement in this way, such as those in processions, quickly grow tired.
χωρὶς μὲν οὖν τοῖς ἔμπροσθεν καὶ ὄπισθεν διὰ ταῦτα οὐ ποιοῦνται τὴν κίνησιν.
It is for these reasons, then, that they do not perform the movement with the front and hind legs separately.
εἰ δὲ τοῖς δεξιοῖς ἀμφοτέροις πρώτοις, ἔξω ἂν ἐγίγνοντο τῶν ἐρεισμάτων καὶ ἔπιπτον ἄν.
But if they moved both right legs first, they would get outside of their supports and would fall.
εἰ δὴ ἀνάγκη μὲν ἢ τούτων τῶν τρόπων ὁποτερονοῦν ποιεῖσθαι τὴν κίνησιν ἢ κατὰ διάμετρον, μὴ ἐνδέχεται δʼ ἐκείνων μηδέτερον, ἀνάγκη κινεῖσθαι κατὰ διάμετρον· οὕτω γὰρ κινούμενα ὥσπερ εἴρηται οὐδέτερα τούτων οἷόν τε πάσχειν.
If indeed it is necessary to make the movement either in one of these ways or diagonally, but neither of those is possible, it is necessary to move diagonally; for moving in this way, as has been said, they can suffer neither of these things.
καὶ διὰ τοῦτο οἱ ἵπποι καὶ ὅσα τοιαῦτα, ἵσταται προβεβηκότα κατὰ διάμετρον, καὶ οὐ τοῖς δεξιοῖς ἢ τοῖς ἀριστεροῖς ἀμφοτέροις ἅμα.
And for this reason horses and suchlike animals stand with their legs advanced diagonally, and not with both right legs or both left legs together.
τὸν αὐτὸν δὲ τρόπον καὶ ὅσα πλείους πόδας ἔχει τεττάρων ποιεῖται τὴν κίνησιν· ἀεὶ γὰρ ἐν τοῖς τέτταρσι τοῖς ἐφεξῆς τὰ ὀπίσθια πρὸς τὰ ἔμπροσθεν κινεῖται κατὰ διάμετρον· δῆλον δʼ ἐπὶ τοῖς βραδέως κινουμένοις.
And in the same way also those that have more than four feet perform their movement; for always, in successive groups of four, the hind legs move diagonally in relation to the front legs; and this is clear in those that move slowly.
καὶ οἱ καρκίνοι δὲ τὸν αὐτὸν τρόπον κινοῦνται· τῶν πολυπόδων γάρ εἰσιν.
And crabs also move in the same way; for they are among the polypods.
ἀεὶ γὰρ καὶ οὗτοι κατὰ διάμετρον κινοῦνται, ἐφʼ ὅπερ ἂν ποιῶνται τὴν πορείαν.
For these also always move diagonally, in whichever direction they make their progress.
ἰδίως γὰρ τοῦτο τὸ ζῷον ποιεῖται τὴν κίνησιν· μόνον γὰρ οὐ κινεῖται ἐπὶ τὸ πρόσθεν τῶν ζῴων, ἀλλʼ ἐπὶ τὸ πλάγιον.
For this animal performs its movement in a peculiar way; for alone of animals it does not move towards the front, but towards the side.
ἀλλʼ ἐπεὶ τοῖς ὄμμασι διώρισται τὸ πρόσθιον, ἡ φύσις πεποίηκεν ἀκολουθεῖν δυναμένους τοὺς ὀφθαλμοὺς τοῖς κώλοις· κινοῦνται γὰρ εἰς τὸ πλάγιον αὐτοῖς, ὥστε τρόπον τινὰ καὶ τοὺς καρκίνους κινεῖσθαι διὰ τοῦτʼ ἐπὶ τὸ ἔμπροσθεν.
But since the front is defined by the eyes, nature has made their eyes able to follow their limbs; for they move to the side for them, so that in a certain way even crabs move towards the front because of this.