OCR Text |
Show 1879.] ANATOMY OF THE HOATZIN. 1 13 strong vinculum downwards to that of the flexor digitorum profundus before it runs on to supply the hallux itself1. The determination of this point the late Prof. C. J. Sundevall much desired2, as in the only specimen he had the opportunity of examining, and that imperfectly, the apparent absence of the vinculum favoured its Passerine affinities. As, however, is stated above, the vinculum is present and large in the individuals dissected by myself. In the upper limb, the great pectoral muscle is much reduced at its furcular and manubrial origins, over which the crop is placed. It is thicker lower down. The fibres of the second pectoral descend as far as the lower margin of the sternum; and there is a small third pectoral covered by it, as in all Gallinae, although in Opisthocomus it is reduced in size. The biceps humeri muscle sends a peculiarly large fasciculus to the tendon of the tensor patagii longus, which reaches it opposite the middle of the patagium3. This slip I never find developed in the Cracidae ; but it is present in the closely allied Megapodidae, and in all the other Gallinaceous birds. The above-mentioned myological facts throw some light on the affinities of Opisthocomus. The presence of two carotid arteries, an ambiens muscle, an accessory femoro-caudal, and a deep plantar vinculum place its non-passerine nature beyond a doubt. Adding the tufted oil-gland and the inch-long colic caeca, the bird could only be related to the Tinamidae, Gallinae, or Rallidae, from which it will be remembered the Cuculidae differ in that they lack the oil-gland tuft, and the Musophagidae in that they have no colic caeca. Opisthocomus, being holorhinal4, can have nothing to do with the Chara-driiform birds. In the Rallidae there is only a single posterior notch on each side of the carina sterni, at the same time that a crop is never developed. These features, when correlated with the peculiarities of the palate, remove them from the necessity of further consideration. Opisthocomus must therefore, from what has been just shown, be a Gallinaceous bird, or form a group by itself. As there is no Gallinaceous bird without a direct articulation between the pterygoid bones and the basisphenoidal rostrum, it is hardly possible to include the Hoatzin along with them; and yet it resembles them most closely, as it does the Cuculidae, in the length of its colic caeca and the number of its rectrices. It is not far removed from the Musophagidae as well. All these facts can be expressed as follows:- 1 Vide P. Z. S. 1875, p. 341. 2 Methodi Naturalis Avium disponendarum Tentamen. Stockholm, 1873, p. 156. 3 Vide P. Z. S. 1876, pp. 195, 199. * P.Z.S. 1873, p. 33. PROC. ZOOL. S O C - 1879, No. VIII. 8 |