This view of the structure of the lung is perfectly correct so far as it extends; and, bearing it in mind, we shall be in a position to understand what Aristotle thought about the passage of air from the lungs into the heart. In every part of the lung, he says, in effect, there is an air tube which is derived from the trachea, and other tubes which are derived from the πόροι which connect the lung with the heart (_suprà_, _C_). Their applied walls constitute the thin “synapses” (τὴν σύναψιν) through which the air passes out of the air tubes into the πόροι, or blood-vessels, by transudation or diffusion; for there is no community between the cavities of the air tubes and cavities of the canals; that is to say, no opening from one into the other (_suprà_, _D_). On the words “κοινὸς πόρος” Aubert and Wimmer remark (_l. c._ p. 239), “Da A. die Ansicht hat die Lungenluft würde dem Herzen zugeführt, so postulirt er statt vieler kleiner Verbindungen einen grossen Verbindungsgang zwischen Lunge und Herz.” But does Aristotle make this assumption? The only evidence so far as I know in favour of the affirmative answer to this question is the following passage:— “Συνήρτεται δὲ καὶ ἡ καρδία τῇ ἀρτηριᾷ πιμελώδεσι καὶ χονδρώδεσι καὶ ἰνώδεσι δεσμοῖς· ᾗ δὲ συνήρτεται, κοῖλόν ἐστιν. φυσωμένης δὲ τῆς ἀρτηρίας μὲν ἐνίοις ἐν οὐ κατάδηλον ποιεῖ, ἐν δὲ τοῖς μείζοσι τῶν ζῴων δῆλον ὅτι εἰσέρχεται τὸ πνεῦμα εἰς αὐτὴν” (i. cap. 16). “The heart and the windpipe are connected by fatty and cartilaginous and fibrous bands; where they are connected it is hollow. Blowing into the windpipe does not show clearly in some animals, but in the larger animals it is clear that the air goes into it.” Aubert and Wimmer give a somewhat different rendering of this passage:— “Auch das Herz hängt mit der Luftröhre durch fettreiche, knorpelige und faserige Bänder zusammen; und da, wo sie zusammenhängen, ist eine Höhlung. Beim Aufblasen der Lunge wird es bei manchen Thieren nicht wahrnehmbar, bei den grösseren aber ist es offenbar, dass die Luft in das Herz gelangt.” The sense here turns upon the signification which is to be ascribed to εἰς αὐτὴν. But if these words refer to the heart, then Aristotle has distinctly pointed out the road which the air, in his opinion, takes, namely, through the “synapses” (_D_); and there is no reason that I can discover to believe that he “postulated” any other and more direct communication. With respect to the meaning of κοῖλόν ἐστιν, Aubert and Wimmer observe:— “Dies scheint wohl die kurze Lungenvene zu sein. Schneider bezieht dies auf die Vorkammern, allein diese werden unten als Höhlen des Herzens beschrieben.”