HOACTZIN, or Hoatzin, a bird of tropical South America, thought by Buffon to be that indicated by Hernandez or Fernandez under these names, the Opisthocomus hoazin or 0. cristatus of modern ornithologists a very curious and remarkable form, which has long exercised the ingenuity of classifiers. Placed by Buffon among his "Ifoccos" (Curassows), and then by P. L. S. Mtiller and Gmeliu in the Linnseau genus Phasianus, some of its many peculiarities were recognized by Illiger in 1811 as sufficient to establish it as a distinct genus, Opisthocomns ; but various positions were assigned to it by subsequent systematic authors, whose views, not being based on any infor mation respecting its internal structure, do not here require particular attention. L Herminier was the first to give any account of its anatomy (Comptes Rendns, 1837, v. p, 433), and from, his time our knowledge of it has been successively increased by Johannes Miiller (Eer. Akad. Wissensch. Berlin, 1841, p. 177), Deville (Rev. et May. de Zoologir, 1852, p. 217),Gervais (Castelnau, Exped. Amerique du Sud, Zoologie, Anatomie, p. 6(5), Prof. Huxley (Proc. Zool. Society, 1868, ]>. 304), Mr Perrin (Trans. Zool. Society, ix. p. 353), and Gal-rod (Proc. Zool. Society, 1870, p. 109). After a minute description of the skeleton of Opisthocomus, with the especial object of determining its affinities, Prof. Huxley declared that it " resembles the ordinary Gallina ceous birds and Pigeons more than it does any others, and that when it diverges from them it is either sui generis or approaches the Musophagidce" He accordingly regarded it as the type and sole member of a group, named by him Heteromorphce, which sprang from the great Carinate stem later than the Tinamomorphce, Turnicomorpkoe, or Chara- driomorphce, but before the Peristeromorphw, Pteroclo- morplive, or Alectoromorphce. This conclusion is substan tially the same as that at which Garrod subsequently arrived after closely examining and dissecting specimens preserved in spirit ; but the latter has gone further and endeavoured to trace more particularly the descent of this peculiar form and some others, remarking that the ancestor of Opistho comus must have left the parent stem very shortly before the true Gallince first appeared, and at about the same time as the independent pedigree of the Cundidce and Muso- phagidoe commenced these two groups being, he believed, very closely related, and Opisthoconms serving to fill the gap between them.
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Hoactzin.
It would be impossible here to state at length the facts on which these views are grounded, and equally impossible to give more than a very few details of the anatomy of this singular form. The first thing that strikes the spectator of its skeleton is the extraordinary structure of the sternal apparatus, which is wholly unlike that of any other bird known. The keel is only developed on the posterior part of the sternum the fore part being, as it were, cut away, while the short furcula at its symphysis meets the manubrium, with which it is firmly consolidated by means of a prolonged and straight hypocleidium, and anteriorly ossifies with the coracoids. This unique arrange ment seems to be correlated with the enormously capacious crop, which rests upon the furcula and fore part of the sternum, and is also received in a cavity formed on the surface of each of the great pectoral muscles. Furthermore this crop is extremely muscular, so as more to resemble a gizzard, and consists of two portions divided by a partial constriction, after a fashion of which no other example is known among birds.