Hippocrates of Cos, On Flesh 608
“Speaking is possible because of air, when someone pulls it into their whole body but especially down into the hollow spaces. When this air is forced to exit through the empty place, it makes a sound because the head echoes. The tongue shapes the sound by touching: as it turns in the throat and closes the palate or the teeth it brings clarity to the sounds. If the tongue does not make the sound sharper by touching each time, the person can’t speak clearly, but, utters only sounds as they are in nature.
An indication of the truth of this is that people who are deaf from birth do not know how to speak but make only simple sounds. It is also not possible to speak after you have breathed out all your air. This is clear: whenever people want to speak loud, they draw in a great breath which they force out of their mouth and they can make a great sound as long as the breath remains. Then, their sound diminishes.”
Διαλέγεται δὲ διὰ τὸ πνεῦμα ἕλκων εἴσω πᾶν τὸ σῶμα, | τὸ πλεῖστον δὲ ἐς τὰ κοῖλα αὐτὸς ἑωυτῷ· αὐτὸ δὲ θύραζε ὠθεόμενον διὰ τὸ κενὸν ψόφον ποιέει· ἡ κεφαλὴ γὰρ ἐπηχεῖ. ἡ δὲ γλῶσσα ἀρθροῖ προσβάλλουσα· ἐν τῷ φάρυγγι ἀποφράσσουσα καὶ προσβάλλουσα πρὸς τὴν ὑπερῴην καὶ πρὸς τοὺς ὀδόντας ποιέει σαφηνίζειν· ἢν δὲ μὴ ἡ γλώσση ἀρθροῖ προσβάλλουσα ἑκάστοτε, οὐκ ἂν σαφέως διαλέγοιτο, ἀλλ᾿ ᾗ ἕκαστα φύσει τὰ μονόφωνα. τεκμήριον δέ ἐστι τούτῳ, οἱ κωφοὶ οἱ ἐκ γενεῆς οὐκ ἐπίστανται διαλέγεσθαι, ἀλλὰ τὰ μονόφωνα μοῦνον φωνέουσιν. οὐδ᾿ εἴ τις τὸ πνεῦμα ἐκπνεύσας πειρῷτο διαλέγεσθαι· δῆλον δὲ τόδε· οἱ ἄνθρωποι ὁκόταν βούλωνται μέγα φωνῆσαι, ἕλκοντες τὸ πνεῦμα τὸ ἔξω ὠθέουσι θύραζε καὶ φθέγγονται μέγα ἕως ἂν ἀντέχῃ τὸ πνεῦμα, ἔπειτα δὲ καταμαραίνεται τὸ φθέγμα·