And for this reason, if the apparatus of the organs of sense should be closed and sleep hindered by some occupation, the nervous system, becoming filled with the vapours, is naturally and spontaneously extended so that the part which has had its density increased by the vapours is rarefied by the process of extension, just as those do who squeeze the water out of clothes by vehement wringing: and, seeing that the parts about the pharynx are somewhat circular, and nervous tissue abounds there, whenever there is need for the expulsion from that part of the density of the vapours-since it is impossible that the part which is circular in shape should be separated directly, but only by being distended in the outline of its circumference-for this reason, by checking the breath a yawn the chin is moved downwards so as to leave a hollow to the uvula, and all the interior parts being arranged in the figure of a circle, that smoky denseness which had been detained in the neighbouring parts is emitted together with the exit of the breath. And often the like may happen even after sleep when any portion of those vapours remains in the region spoken of undigested and unexhaled.

Καὶ τούτου χάριν εἰ στενοχωροῖτο μὲν ὑπὸ τῆς ἔνδοθεν ἀναθυμιάσεως ἡ περὶ τὰ αἰσθητήρια διασκευή͵ κωλύοιτο δὲ κατά τινα χρείαν ὁ ὕπνος, πλῆρες γενόμενον τῶν ἀτμῶν τὸ νευρῶδες͵ αὐτὸ ὑφ' ἑαυτοῦ φυσικῶς διατείνεται͵ ὡς διὰ τῆς ἐκτάσεως τὸ παχυνθὲν ὑπὸ τῶν ἀτμῶν μέρος ἐκλεπτυνθῆναι, οἷόν τι ποιοῦσιν οἱ διὰ τῆς σφοδροτέρας στρεβλώσεως τὸ ὕδωρ τῶν ἱματίων ἐκθλίβοντες. Καὶ ἐπειδὴ κυκλοτερῆ τὰ περὶ τὸν φάρυγγα μέρη͵ πλεονάζει δὲ τὸ νευρῶδες ἐν τούτοις, ὅταν καὶ ἀπὸ τούτων ἐξωσθῆναι δέοι τὴν τῶν ἀτμῶν παχυμέρειαν (ἐπειδὴ ἀμήχανόν ἐστι δι' εὐθείας ἀποτεῖναι τὸ κυκλοειδὲς μέρος͵ εἰ μὴ κατὰ τὸ περιφερὲς σχῆμα διαταθείη), τούτου χάριν ἀποληφθέντος ἐν τῇ χάσμῃ τοῦ πνεύματος͵ ὅτε ὁ ἀνθερεὼν ἐπὶ τὸ κάτω τοῖς γαργαρεῶσιν ὑποκοιλαίνεται καὶ τῶν ἐντὸς πάντων εἰς κύκλου σχῆμα διαταθέντων͵ ἡ λιγνυώδης ἐκείνη παχύτης ἡ ἐναπειλημμένη τοῖς μέρεσι συνδιαπνεῖται τῇ διεξόδῳ τοῦ πνεύματος. Πολλάκις δὲ καὶ μετὰ τὸν ὕπνον οἶδε τὸ τοιοῦτον συμβαίνειν͵ ὅταν τι τῶν ἀτμῶν ἐκείνων περιλειφθείη τοῖς τόποις ἄπεμπτόν τε καὶ ἀδιάπνευστον.