The clavicles, when united, as usual, form the furcula; mostly the distal median portion is drawn out into a hypocleidium of various shape.
In some of those birds which have a peculiarly harsh or trumpeting voice, the trachea is lengthened, forming loops which lie subcutaneously (capercally, curassow), or it enters and dilates the symphysis of the furcula (crested guineafowl); or, e.g.
The keel is pushed back to the distal third of the sternum, whilst the original anterior margin of the keel is correspondingly elongated,and the furcula fused with the rostral portion.
He concisely cites (p. 238) no fewer than eight other characters of more or less value as peculiar to the Carinate Division, the first of which is that the feathers have their barbs furnished with hooks, in consequence of which the barbs, including those of the wing-quills, cling closely together; while among the rest may be mentioned the position of the furcula and coracoids, 4 which keep the wing-bones apart; the limitation of the number of the lumbar vertebra to fifteen, and of the carpals to two; as well as the divergent direction of the iliac bones - the corresponding characters peculiar to the Ratite Division being the disconnected condition of the barbs of the feathers, through the absence of any hooks whereby they might cohere; the non-existence of the furcula, and the coalescence of the coracoids with the scapulae (or, as he expressed it, the extension of the scapulae to supply the place of the coracoids, which he thought were wanting); the lumbar vertebrae being twenty and the carpals three in number; and the parallelism of the iliac bones.
4 Merrem, as did many others in his time, calls the coracoids "clavicultiae "; but it is now well understood that in birds the real claviculae form the furcula or " merry-thought."
But the latter used this privilege wisely and well-not, after the manner of De Blainville and others subsequent to him, relying solely or even chiefly on the character afforded by the posterior portion of the sternum, but taking also into consideration those of the anterior, as well as of the in some cases still more important characters presented by the pre-sternal bones, such as the furcula, coracoids and scapulae.
The furcula is complete and strong, the feet very passerine in appearance.
Its furcula has been said (Proc. Zool.
This bird, apparently mentioned by Marcgrave more than 200 years ago, but first described by Pallas, is remarkable for the structure - unique, if not possessed by its representative forms - of its furcula, where the head, instead of being .the thin plate found in all other Gallinae, is a hollow cup opening upwards, into which the trachea dips, and then emerges on its way to the lungs.
Scarcely anything is known of the sternum, and little of the shoulder-girdle, except the very stout furcula; scapula typically bird-like.