Note 84 — PROGRESSION IN OR THROUGH THE AIR. (continued 2)

The furcula are usually united to the anterior part of the sternum by ligament; but in birds of powerful flight, where the wings are habitually extended for gliding and sailing, as in the frigate-bird, the union is osseous in its nature. “In the frigate-bird the furcula are likewise anchylosed with the coracoid bones.”—Comp. Anat. and Phys. of Vertebrates, by Prof. Owen, vol. ii. p. 66.