Divisions of the Pulmonary Artery and Veins, and thereby lengthens and enlarges their Cavities.
This enlargement of their Cavities is very considerable, not only upon the score of the addition, which they receive in length thereby, but also upon the account of their Divarication. For whereas, when the Ribs are depress'd, and the Lungs subside, the Blood-vessels are not only contracted, (as I have already observ'd) but their Branches, which are exceeding numerous, approach one another,
and lie in juxta-position, by which their Cavities are very much compress'd and streighten'd: When the Ribs are elevated, and the Lungs turgid with Air, not only the Fibres, by which their Coats in the opposite state were contracted, are extended; but those innumerable Vessels, which lying before in lines almost parallel upon one another, compress'd one another, making an acute Angle at their Junctures, are divaricated and separated from each other, and make an obtuse, whereby their Channels are widened.
Thus a passage is open'd to the Blood, from