While resting, then, the whole weight of the body on this substance of the bones, as on some columns that carry a mass of building, she did not implant the bone undivided through the whole structure: for in that case man would have remained without motion or activity, if he had been so constructed, just like a tree that stands on one spot without either the alternate motion of legs to advance its motion or the service of hands to minister to the conveniences of life: but now we see that she contrived that the instrument should be rendered capable of walking and working by this device, after she had implanted in the body, by the determining spirit which extends through the nerves, the impulse and power for motion. And hence is produced the service of the hands, so varied and multiform, and answering to every thought. Hence are produced, as though by some mechanical contrivance, the turnings of the neck, and the bending and raising of the head, and the action of the chin, and the separation of the eyelids, that takes place with a thought, and the movements of the other joints, by the tightening or relaxation of certain nerves. And the power that extends through these exhibits a sort of independent impulse, working with the spirit of its will by a sort of natural management, in each particular part; but the root of all, and the principle of the motions of the nerves, is found in the nervous tissue that surrounds the brain.

Ταύτῃ τοίνυν τῇ στεῤῥᾷ τῶν ὀστέων φύσει͵ οἷον στύλοις τισὶν ἀχθοφόροις͵ ὅλον τοῦ σώματος ἐπιθεῖσα τὸ βάρος͵ οὐκ ἀδιαίρετον ἐνέφυσε τῷ παντὶ τὸ ὀστέον. ῏Η γὰρ ἂν ἀκίνητός τε καὶ ἀνενέργητος ἔμεινεν͵ εἰ οὕτω κατασκευῆς εἶχεν ὁ ἄνθρωπος͵ καθάπερ τι δένδρον ἐφ' ἑνὸς τόπου μένον͵ μήτε τῆς τῶν σκελῶν διαδοχῆς ἐπὶ τὸ πρόσω προαγούσης τὴν κίνησιν͵ μήτε τῆς τῶν χειρῶν ὑπουργίας χρησιμευούσης τῷ βίῳ. Νυνὶ δὲ μεταβατικὸν εἶναι καὶ πρακτικὸν τὸ ὄργανον διὰ τῆς ἐπινοίας ταύτης ἐμηχανήσατο͵ τῷ προαιρετικῷ πνεύματι τῷ διὰ τῶν νεύρων διήκοντι͵ τὴν πρὸς τὰς κινήσεις ὁρμήν τε καὶ δύναμιν ἐνθεῖσα τῷ σώματι. Ἐντεῦθεν ἡ τῶν χειρῶν ὑπουργία͵ ἡ ποικίλη τε καὶ πολύστροφος καὶ πρὸς πᾶσαν ἐπίνοιαν ἐπιτηδεία. Ἐντεῦθεν αἱ τοῦ αὐχένος περιστροφαὶ καὶ τῆς κεφαλῆς ἐπικλίσεις τε καὶ ἀνανεύσεις καὶ ἡ κατὰ τὴν γένην ἐνέργεια καὶ ἡ τῶν βλεφάρων διαστολὴ ἅμα νεύματι γινομένη καὶ τῶν λοιπῶν ἄρθρων αἱ κινήσεις ἐν νεύροις μέν τισιν ἀνασπωμένοις ἢ χαλωμένοις͵ καθάπερ ἐκ μηχανῆς τινος ἐνεργοῦνται. Ἡ δὲ διὰ τούτων διεξιοῦσα δύναμις αὐτοκέλευστον ἔχει τινὰ τὴν ὁρμήν͵ προαιρετικῷ πνεύματι κατά τινα φύσεως οἰκονομίαν ἐν τοῖς καθέκαστον ἐνεργουμένη. Ρίζα δὲ πάντων ἀπεδείχθη καὶ ἀρχὴ τῶν κατὰ τὰ νεῦρα κινήσεων ὁ τὸν ἐγκέφαλον περιέχων νευρώδης ὑμήν.