And next, they ordered the water-courses of the body in a manner which I will describe, and which will be more easily understood if we begin by admitting that all things which have lesser parts retain the greater, but the greater cannot retain the lesser. Now of all natures fire has the smallest parts, and therefore penetrates through earth and water and air and their compounds, nor can anything hold it. And a similar principle applies to the human belly; for when meats and drinks enter it, it holds them, but it cannot hold air and fire, because the particles of which they consist are smaller than its own structure.

These elements, therefore, God employed for the sake of distributing moisture from the belly into the veins, weaving together network of fire and air like a weel, having at the entrance two lesser weels; further he constructed one of these with two openings, and from the lesser weels he extended cords reaching all round to the extremities of the network. All the interior of the net he made of fire, but the lesser weels and their cavity, of air. The network he took and spread over the newly-formed animal in the following manner:-He let the lesser weels pass into the mouth; there were two of them, and one he let down by the air-pipes into the lungs, the other by the side of the air-pipes into the belly. The former he divided into two branches, both of which he made to meet at the channels of the nose, so that when the way through the mouth did not act, the streams of the mouth as well were replenished through the nose. With the other cavity (i.e. of the greater weel) he enveloped the hollow parts of the body, and at one time he made all this to flow into the lesser weels, quite gently, for they are composed of air, and at another time he caused the lesser weels to flow back again; and the net he made to find a way in and out through the pores of the body, and the rays of fire which are bound fast within followed the passage of the air either way, never at any time ceasing so long as the mortal being holds together.

[78a] τὸ δ΄ ἐντεῦθεν ἤδη τὴν ὑδραγωγίαν παρεσκεύασαν τρόπῳ τινὶ τοιῷδε͵ ὃν κατοψόμεθα ῥᾷον προδιομολογησάμενοι τὸ τοιόνδε͵ ὅτι πάντα ὅσα ἐξ ἐλαττόνων συνίσταται στέγει τὰ μείζω͵ τὰ δὲ ἐκ μειζόνων τὰ σμικρότερα οὐ δύναται͵ πῦρ δὲ πάντων γενῶν σμικρομερέστατον͵ ὅθεν δι΄ ὕδατος καὶ γῆς ἀέρος τε καὶ ὅσα ἐκ τούτων συνίσταται διαχωρεῖ καὶ στέγειν οὐδὲν αὐτὸ δύναται. ταὐτὸν δὴ καὶ περὶ τῆς παρ΄ ἡμῖν κοιλίας διανοητέον͵ ὅτι σιτία μὲν καὶ ποτὰ ὅταν εἰς αὐτὴν ἐμπέσῃ͵ στέγει͵ [78b] πνεῦμα δὲ καὶ πῦρ σμικρομερέστερα ὄντα τῆς αὑτῆς συστάσεως οὐ δύναται.  

τούτοις οὖν κατεχρήσατο ὁ θεὸς εἰς τὴν ἐκ τῆς κοιλίας ἐπὶ τὰς φλέβας ὑδρείαν͵ πλέγμα ἐξ ἀέρος καὶ πυρὸς οἷον οἱ κύρτοι συνυφηνάμενος͵ διπλᾶ κατὰ τὴν εἴσοδον ἐγκύρτια ἔχον͵ ὧν θάτερον αὖ πάλιν διέπλεξεν δίκρουν· καὶ ἀπὸ τῶν ἐγκυρτίων δὴ διετείνατο οἷον σχοίνους κύκλῳ διὰ παντὸς πρὸς τὰ ἔσχατα τοῦ πλέγματος. [78c] τὰ μὲν οὖν ἔνδον ἐκ πυρὸς συνεστήσατο τοῦ πλοκάνου ἅπαντα͵ τὰ δ΄ ἐγκύρτια καὶ τὸ κύτος ἀεροειδῆ͵ καὶ λαβὼν αὐτὸ περιέστησεν τῷ πλασθέντι ζῴῳ τρόπον τοιόνδε. τὸ μὲν τῶν ἐγκυρτίων εἰς τὸ στόμα μεθῆκεν· διπλοῦ δὲ ὄντος αὐτοῦ κατὰ μὲν τὰς ἀρτηρίας εἰς τὸν πλεύμονα καθῆκεν θάτερον͵ τὸ δ΄ εἰς τὴν κοιλίαν παρὰ τὰς ἀρτηρίας· τὸ δ΄ ἕτερον σχίσας τὸ μέρος ἑκάτερον κατὰ τοὺς ὀχετοὺς τῆς ῥινὸς ἀφῆκεν κοινόν͵ ὥσθ΄ ὅτε μὴ κατὰ στόμα ἴοι θάτερον͵ ἐκ τούτου πάντα καὶ τὰ ἐκείνου ῥεύματα ἀναπληροῦσθαι. [78d] τὸ δὲ ἄλλο κύτος τοῦ κύρτου περὶ τὸ σῶμα ὅσον κοῖλον ἡμῶν περιέφυσεν͵ καὶ πᾶν δὴ τοῦτο τοτὲ μὲν εἰς τὰ ἐγκύρτια συρρεῖν μαλακῶς͵ ἅτε ἀέρα ὄντα͵ ἐποίησεν͵ τοτὲ δὲ ἀναρρεῖν μὲν τὰ ἐγκύρτια͵ τὸ δὲ πλέγμα͵ ὡς ὄντος τοῦ σώματος μανοῦ͵ δύεσθαι εἴσω δι΄ αὐτοῦ καὶ πάλιν ἔξω͵ τὰς δὲ ἐντὸς τοῦ πυρὸς ἀκτῖνας διαδεδεμένας ἀκολουθεῖν ἐφ΄ ἑκάτερα ἰόντος τοῦ ἀέρος͵ [78e] καὶ τοῦτο͵ ἕωσπερ ἂν τὸ θνητὸν συνεστήκῃ ζῷον͵ μὴ διαπαύεσθαι γιγνόμενον·