Each of those who uphold these views puts forward some reasons of a more physical character on behalf of his opinion concerning the ruling principle. One declares that the motion which proceeds from the understanding is in some way akin to the nature of fire, because fire and the understanding are alike in perpetual motion; and since heat is allowed to have its source in the region of the heart, he says on this ground that the motion of mind is compounded with the mobility of heat, and asserts that the heart, in which heat is enclosed, is the receptacle of the intelligent nature. The other declares that the cerebral membrane (for so they call the tissue that surrounds the brain) is as it were a foundation or root of all the senses, and hereby makes good his own argument, on the ground that the intellectual energy cannot have its seat save in that part where the ear, connected with it, comes into concussion with the sounds that fall upon it, and the sight (which naturally belongs to the hollow of the place where the eyes are situated) makes its internal representation by means of the images that fall upon the pupils, while the qualities of scents are discerned in it by being drawn in through the nose, and the sense of taste is tried by the test of the cerebral membrane, which sends down from itself, by the veterbrae of the neck, sensitive nerve-processes to the isthmoidal passage, and unites them with the muscles there.

Προστιθέασι δὲ καί τινας φυσικωτέρας αἰτίας τῆς τοιαύτης περὶ τὸ ἡγεμονικὸν ὑπονοίας ἑκάτερος τῶν ταύταις ταῖς δόξαις παρισταμένων. Ὁ μὲν γὰρ πρὸς τὸ πυρῶδες συγγενῶς ἔχειν τὴν ἐκ τῆς διανοίας κίνησιν λέγει͵ διὰ τὸ ἀεικίνητον εἶναι καὶ τὸ πῦρ καὶ τὴν διάνοιαν. Καὶ ἐπειδὴ πηγάζειν ἐν τῷ μορίῳ τῆς καρδίας ἡ θερμότης ὁμολογεῖται, διὰ τοῦτο τῷ εὐκινήτῳ τῆς θερμότητος τὴν τοῦ νοῦ κίνησιν ἀνακεκρᾶσθαι λέγων͵ δοχεῖον τῆς νοερᾶς φύσεως τὴν καρδίαν εἶναί φησιν͵ ἐν ᾗ τὸ θερμὸν περιείληπται. Ὁ δὲ ἕτερος πᾶσι τοῖς αἰσθητηρίοις οἷον ὑποβάθραν τινὰ καὶ ῥίζαν εἶναι λέγει τὴν μήνιγγα (οὕτω γὰρ ὀνομάζουσι τὸν περιεκτικὸν τοῦ ἐγκεφάλου ὑμένα), καὶ τούτῳ πιστοῦνται τὸν ἴδιον λόγον͵ ὡς οὐχ ἑτέρωθι τῆς νοητικῆς ἐνεργείας καθιδρυμένης͵ εἰ μὴ κατ' ἐκεῖνο τὸ μέρος͵ ᾧ καὶ τὸ οὖς ἐφηρμοσμένον τὰς ἐμπιπτούσας αὐτῷ φωνὰς προσαράσσει. Καὶ ἡ ὄψις κατὰ τὸν πυθμένα τῆς τῶν ὀφθαλμῶν ἕδρας συμπεφυκυῖα͵ διὰ τῶν ἐμπιπτόντων ταῖς κόραις εἰδώλων πρὸς τὸ ἔσω ποιεῖται τὴν τύπωσιν. Καὶ τῶν ἀτμῶν αἱ ποιότητες διὰ τῆς τῶν ὀσφρήσεων ὁλκῆς ἐν αὐτῷ διακρίνονται. Καὶ ἡ κατὰ τὴν γεῦσιν αἴσθησις τῇ ἐπικρίσει τῆς μήνιγγος δοκιμάζεται͵ ἐκ τοῦ σύνεγγυς ἐκφύσεις τινὰς νευρώδεις ἀφ' ἑαυτῆς αἰσθητικὰς διὰ τῶν αὐχενίων σπονδύλων ἐπὶ τὸν ἠθμοειδῆ πόρον κατὰ τοὺς αὐτόθι μύας ἐγκαταμιξάσης.