§1Περὶ δὲ τῶν χρησίμων μορίων τοῖς ζῴοις πρὸς τὴν κίνησιν 1 τὴν κατὰ τόπον ἐπισκεπτέον διὰ τίνα αἰτίαν τοιοῦτόν ἐστιν ἕκαστον αὐτῶν καὶ τίνος ἕνεκεν ὑπάρχει αὐτοῖς, ἔτι δὲ περὶ τῶν διαφορῶν τῶν τε πρὸς ἄλληλα τοῖς τοῦ αὐτοῦ καὶ ἑνὸς ζῴου μορίοις καὶ πρὸς τὰ τῶν ἄλλων τῶν τῷ γένει διαφόρων.
Regarding the parts of animals that are useful for their locomotion, we must investigate for what cause each of them is such as it is and for the sake of what it belongs to them; and furthermore, regarding the differences between these parts, both in relation to one another within the same and single animal, and in relation to those of other animals that differ in genus.
πρῶτον δὲ λάβωμεν περὶ ὅσων ἐπισκεπτέον.
First, let us state how many things we must investigate.
ἔστι δὲ αὐτῶν ἓν μὲν πόσοις ἐλαχίστοις τὰ ζῷα κινεῖται σημείοις, ἔπειτα διὰ τί τὰ μὲν ἔναιμα τέτταρσι τὰ δʼ ἄναιμα πλείοσι, καὶ καθόλου δὲ διὰ τίνʼ αἰτίαν τὰ μὲν ἄποδα τὰ δὲ δίποδα τὰ δὲ τετράποδα τὰ δὲ πολύποδα τῶν ζῴων ἐστί, καὶ διὰ τί πάντα ἀρτίους ἔχει τοὺς πόδας, ὅσαπερ ἔχει πόδας αὐτῶν, ὅλως δʼ οἷς κινεῖται σημείοις, ἄρτια ταῦτʼ ἐστιν·
One of them is: by how few points at least animals move; next, why red-blooded animals move by four points, while bloodless animals move by more; and in general, for what cause some animals are footless, some two-footed, some four-footed, and some many-footed, and why all those that have feet have an even number of feet, and in general, the points by which they move are even in number.
ἔτι δὲ διὰ τίνʼ αἰτίαν ἄνθρωπος μὲν καὶ ὄρνις δίπους, οἱ δʼ ἰχθύες ἄποδές εἰσι· καὶ τὰς κάμψεις ὅ τε ἄνθρωπος καὶ ὁ ὄρνις δίποδες ὄντες ἐναντίας ἔχουσι τῶν σκελῶν (ὁ μὲν γὰρ ἄνθρωπος ἐπὶ τὴν περιφέρειαν κάμπτει τὸ σκέλος, ὁ δʼ ὄρνις ἐπὶ τὸ κοῖλον.
Furthermore, for what cause man and bird are two-footed, while fish are footless; and why man and bird, although both are two-footed, have opposite flexions of their legs (for man bends his leg toward the convex circumference, while the bird bends it toward the concave.
καὶ ὁ ἄνθρωπος αὐτὸς ἑαυτῷ ἐναντίως τὰ σκέλη καὶ τοὺς βραχίονας· τοὺς μὲν γὰρ ἐπὶ τὸ κοῖλον, τὰ δὲ γόνατα ἐπὶ τὴν περιφέρειαν κάμπτει.
And man bends his legs and arms in opposite directions to each other, for he bends his arms toward the concave, but his knees toward the convex.
καὶ τὰ τετράποδα τὰ ζῳοτόκα τοῖς τʼ ἀνθρώποις ἐναντίως κάμπτει καὶ αὐτὰ αὐτοῖς· τὰ μὲν γὰρ πρόσθια σκέλη ἐπὶ τὸ κυρτὸν τῆς περιφερείας κάμπτει, τὰ δʼ ὀπίσθια ἐπὶ τὸ κοῖλον.
And viviparous quadrupeds bend their limbs in a way opposite to man and also opposite within themselves; for they bend their front legs toward the convex part of the circumference, and their hind legs toward the concave.
ἔτι δὲ τῶν τετραπόδων ὅσα μὴ ζῳοτοκεῖ ἀλλʼ ᾠοτοκεῖ, ἰδίως καὶ εἰς τὸ πλάγιον κάμπτει) πρὸς δὲ τούτοις διὰ τίνʼ αἰτίαν τὰ τετράποδα κινεῖται κατὰ διάμετρον περὶ δὴ πάντων τούτων, καὶ ὅσα ἄλλα συγγενῆ τούτοις, τὰς αἰτίας θεωρητέον.
Furthermore, of those quadrupeds that are not viviparous but oviparous, they bend them in a peculiar way and sideways); and in addition to these, for what cause quadrupeds move diagonally. Indeed, about all these and whatever other things are akin to them, we must contemplate the causes.
ὅτι μὲν οὖν οὕτω ταῦτα συμβαίνει, δῆλον ἐκ τῆς ἱστορίας τῆς φυσικῆς, διότι δέ, νῦν σκεπτέον.
That these things happen in this way is clear from the natural history; but for what reason they do so, we must now investigate.
§22 Ἀρχὴ δὲ τῆς σκέψεως ὑποθεμένοις οἷς εἰώθαμεν χρῆσθαι πολλάκις πρὸς τὴν μέθοδον τὴν φυσικήν, λαβόντες τὰ τοῦτον ἔχοντα τὸν τρόπον ἐν πᾶσι τοῖς τῆς φύσεως ἔργοις, τούτων δʼ ἓν μέν ἐστιν ὅτι ἡ φύσις οὐθὲν ποιεῖ μάτην, ἀλλʼ ἀεὶ ἐκ τῶν ἐνδεχομένων τῇ οὐσίᾳ περὶ ἕκαστον γένος ζῴου τὸ ἄριστον·
The starting point of the inquiry is to assume the principles we are accustomed to use frequently in our method of natural science, taking things that are in this way in all the works of nature.
διόπερ εἰ βέλτιον ὡδί, οὕτως καὶ ἔχει κατὰ φύσιν.
One of these is that nature does nothing in vain, but always does what is best from among the possibilities for the substantial being of each genus of animal; therefore, if it is better in this way, it is also in this way according to nature.
ἔτι τὰς διαστάσεις τοῦ μεγέθους, πόσαι καὶ ποῖαι ποίοις ὑπάρχουσι, δεῖ λαβεῖν.
Furthermore, we must grasp the dimensions of magnitude, how many and of what kind they are, and to what things they belong.
εἰσὶ γὰρ διαστάσεις μὲν ἕξ, συζυγίαι δὲ τρεῖς, μία μὲν τὸ ἄνω καὶ τὸ κάτω, δευτέρα δὲ τὸ ἔμπροσθεν καὶ τὸ ὄπισθεν, τρίτη δὲ τὸ δεξιὸν καὶ τὸ ἀριστερόν.
For there are six dimensions and three pairs: first, up and down; second, front and back; third, right and left.
πρὸς δὲ τούτοις ὅτι τῶν κινήσεων τῶν κατὰ τόπον ἀρχαὶ ὦσις καὶ ἕλξις.
In addition to these, we must assume that of locomotions, the principles are pushing and pulling.
καθʼ αὐτὰς μὲν οὖν αὗται, κατὰ συμβεβηκὸς δὲ κινεῖται τὸ φερόμενον ὑπʼ ἄλλου· οὐ γὰρ αὐτὸ δοκεῖ κινεῖν αὐτό, ἀλλʼ ὐπʼ ἄλλου κίνεῖσθαι τὸ ὑπό τινος φερόμενον.
These are principles in themselves, whereas what is carried by something else is moved accidentally; for it does not seem to move itself, but to be moved by another, namely that which is carried by something.
§33 Τούτων δὲ διωρισμένων λέγωμεν τὰ τούτων ἐφεξῆς.
These things having been defined, let us speak of what follows from them.
τῶν δὴ ζῴων ὅσα μεταβάλλει κατὰ τόπον, τὰ μὲν ἀθρόῳ. παντὶ τῷ σώματι μεταβάλλει, καθάπερ τὰ ἁλλόμενα, τὰ δὲ μορίοις, καθάπερ τῶν πορευομένων ἕκαστον.
Of those animals that change their place, some change with their whole body all at once, like jumping things, and others by parts, like each of those that walk.
ἐν ἀμφοτέραις δὲ ταῖς μεταβολαῖς ταύταις ἀεὶ μεταβάλλει τὸ κινούμενον ἀποστηριζόμενον πρὸς τὸ ὑποκείμενον αὐτῷ.
In both of these changes, the moving thing always changes its place by supporting itself against what lies beneath it.
διόπερ ἐάν τε ὑποφέρηται τοῦτο θᾶττον ἢ ὥστʼ ἔχειν ἀπερείσασθαι τὸ ποιούμενον ἐπʼ αὐτοῦ τὴν κίνησιν, ἐάν θʼ ὅλως μηδεμίαν ἔχῃ τοῖς κινουμένοις ἀντέρεισιν, οὐθὲν ἐπʼ αὐτοῦ δύναται κινεῖν ἑαυτό.
Therefore, if this under-surface slips away faster than the thing making its movement upon it can support itself, or if it has absolutely no resistance for the moving things, nothing can move itself upon it.
καὶ γὰρ τὸ ἁλλόμενον καὶ πρὸς αὐτὸ ἀπερειδόμενον τὸ ἄνω καὶ πρὸς τὸ ὑπὸ τοὺς πόδας ποιεῖται τὴν ἅλσιν· ἔχει γάρ τινα ἀντέρεισιν πρὸς ἄλληλα τὰ μόρια ἐν ταῖς καμπαῖς, καὶ ὅλως τὸ πιέζον πρὸς τὸ πιεζόμενον.
For even the jumping thing makes its jump by supporting itself both against its own upper part and against what is under its feet; for the parts have some resistance to one another in the flexions, and in general, the pressing part against the pressed.
διὸ καὶ οἱ πένταθλοι ἅλλονται πλέον ἔχοντες τοὺς ἁλτῆρας ἢ μὴ ἔχοντες, καὶ οἱ θέοντες θᾶττον θέουσι παρασείοντεσ τὰς χεῖρας· γίνεται γάρ τις ἀπέρεισις ἐν τῇ διατάσει πρὸς τὰς χεῖρας καὶ τοὺς καρπούς.
For this reason, pentathletes jump further when they have weights than when they do not, and runners run faster when they swing their hands; for some support is created in the extension against the hands and wrists.
ἀεὶ δὲ τὸ κινούμενον δυσὶν ἐλαχίστοις χρώμενον ὀργανικοῖς μέρεσι ποιεῖται τὴν μεταβολήν, τῷ μὲν ὡσπερανεὶ θλίβοντι, τῷ δὲ θλιβομένῳ.
And the moving thing always makes its change of place by using at least two organic parts, one as it were pressing, and the other pressed.
τὸ μὲν γὰρ μένον θλίβεται διὰ τὸ φέρειν, τὸ δʼ αἰρόμενον τείνεται τῷ φέροντι τὸ φορτίον.
For that which remains stationary is pressed because of carrying, while that which is lifted is extended by that which carries the load.
διόπερ ἀμερὲς οὐδὲν οὕτω κινηθῆναι δυνατόν· οὐ γὰρ ἔχει τήν τε τοῦ πεισομένου καὶ τὴν τοῦ ποιήσοντος ἐν αὑτῷ διάληψιν.
Therefore, nothing without parts can move in this way; for it does not have within itself the distinction between that which is to be acted upon and that which is to act.