Note g — BOOK VII.

It is no less remarkable in Birds, that their Lungs adhere to the Thorax, and have but little play, than that to other Animals they are loose, and play much, which is a good Provision for their steady Flight. Also they want the Diaphragm, and instead thereof, have divers large Bladders made of thin transparent Membranes, with pretty large Holes out of one into the other. These Membranes seem to me to serve for Ligaments, or Braces to the Viscera, as well as to contain Air. Towards the upper Part, each Lobe of the Lungs is perforated in two Places, with large Perforations; whereof one is towards the outer, the other towards the inner Part of the Lobe. Through these Perforations, the Air hath a Passage into the Belly, (as in Book I. Chap. 1. Note (b);) that is, into the foremention’d Bladders; so that by blowing into the aspera Arteria, the Lungs will be a little rais’d, and the whole Belly blown up, so as to be very turgid. Which doubtless is a Means to make their Bodies more or less buoyant, according as they take in more or less Air, to facilitate thereby, their Ascents, and Descents: Like as it is in the Air-bladders of Fishes, in the last cited Place. Note (i).