1868.] PROF. IIUXLEY ON THE ALECTOROMORPHyE. 305 



In my paper on the Classification of Birds I have described the 

 palate of OpistJiocomus (p. 435), and have shown that it has an Alec- 

 toromorphic tarso-metatarsus (p. 4(i0) ; bnt I have expressed the 

 opinion that its other pecuUarities necessitate the placing of the bird 

 in a special division of the Schizognathce. At the same time, I men- 

 tioned 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 my materials, with a liberality and courtesy for which I gladly 

 express myself his debtor, placed an excellent mounted skeleton and 

 some detached bones of the Hoazin, in his collection, at my disposi- 

 tion ; 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 investiga- 

 tion 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 Musophayidce. 



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 ascer- 

 tainable. 



In the large number of its cervical vertebrae, Opisthocomus is un- 

 like any of the birds belonging to the groups which have already 

 been discussed; Timtmus, however, has 18 cervicals. 



The two or three last cervical vertebrae are aukylosed with one 

 another and with the two anterior dorsals*. 



The third dorsal is free ; but the fourth and fifth are united toge- 

 ther 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 Alectoromorpha, Pteroclomorphce, and PensteromorjihcB, 

 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 anky- 

 losis 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 ver- 

 tebra bears small and slender ribs ; of the nineteenth the ribs are 

 broader, but have no unciform process In Mr. Ey ton's specimen 

 the seventeenth cervical has short ribs ; the eighteenth a broader 

 and longer rib, with a rudimentary miciform process ; and the 

 * In Mr. Eyton's specimen the second dorsal appears to be free. 



Proc. Zool. Soc. — 18(/8, No. XX. 



