OCR Text |
Show 1868.] PROF. HUXLEY ON THE ALECTOROMORPHAE. 305 In my paper on the Classification of Birds I have described the palate of Opisthocomus (p. 435), and have shown that it has an Alec-toromorphic tarso-metatarsus (p. 460) ; but I have expressed the opinion that its other peculiarities necessitate the placing of the bird in a special division of the Schizognathce. At the same time, I mentioned that this opinion was based upon the examination of only an incomplete skull and the bones of the feet. M . Alphonse Milne-Edwards, noting this indication of the paucity of m y materials, with a liberality and courtesy for which I gladlv express myself his debtor, placed an excellent mounted skeleton and some detached bones of the Hoazin, in his collection, at m y disposition ; and Mr. Eyton, with no less kindly readiness, has supplied me with another mounted skeleton of the same bird. I have thus been enabled to make a tolerably complete investigation of its osteology, the result of which has been entirely to confirm the conclusions of L'Herminier, that Opisthocomus resembles the Fowls and the Pigeons in almost all those respects in which it is like other birds, while in many points it is altogether peculiar, and only in one or two features resembles the Musophagidee. I find the number of the vertebrae to be 19 cervical, 5 dorsal, 3 lumbar, 4 sacral, 6 urosacral, and 4 free caudal. To these succeeds the pygostyle, the number of the vertebrae in which is not ascertainable. In the large number of its cervical vertebrae, Opisthocomus is unlike any of the birds belonging to the groups which have already been discussed; Tinamus, however, has 18 cervicals. The two or three last cervical vertebrae are ankylosed with one another and with the two anterior dorsals*. The third dorsal is free ; but the fourth and fifth are united together and with the succeeding vertebrae to form the " sacrum," and are overlapped by the ilia. Thus it is the antepenultimate (and not the penultimate) dorsal which is free; and in this respect Opisthocomus differs not only from all the Alectoromorphce, Pteroclomorphce, and Peristeromorphce, but from the only other birds (the Falcons and Flamingos) in which a similar ankylosis of the hindermost cervical with more or fewer of the anterior dorsal vertebrae takes place. In Corythaix no ankylosis occurs. Only the hindermost six or seven cervical vertebrae have median inferior crests, and these are very weak; the inferior faces of the centra of the dorsal vertebrae are all flattened and devoid of crests. In this respect Opisthocomus departs alike from the Gallinaceous birds and the Touracos, and,* indeed, from the great majority of its class. In M . A. Milne-Edwards's specimen the eighteenth cervical vertebra bears small and slender ribs ; of the nineteenth the ribs are broader, but have no unciform process In Mr. Eyton's specimen the seventeenth cervical has short ribs ; the eighteenth a broader and longer rib, with a rudimentary unciform process; and the * In M r . Eyton's specimen the second dorsal appears to be free. P R O C ZOOL. Soc-1868, No. XX. |