OCR Text |
Show 1876.] ANATOMY OF CHAUNA DERBIANA. 197 Screamer more closely approaches. It evidently does not share the peculiarities of the former, in all species of which the surface of origin for the pair of large extensor muscles of the mandible is characteristically compressed from side to side, and elongated from above downwards, at the same time that there is the pair of openings above the foramen magnum (figs. 1, 2, 3, p. 198). Again, from a comparison of the inferior surfaces of the same three skulls, it is equally evident that in the Screamer the praemaxillae, maxillaries, and dentaries agree with the same bones in the Gallinaceous bird in not being large and outspreading. The palate of Chauna is represented in fig. 4. In the Screamers the skull is, no doubt, as in the Anseres, desmognathous, having the maxillo-palatines united across the middle line ; but this character is not sufficiently important, to compel us to unite the two groups ; for if such were the case it would be necessary to give credence to an association of birds which is in other respects extremely unnatural. In the Capitonidae, for instance, Megalama is not desmognathous, whilst Tetragonops is so. As before stated, in the Anserine birds the lachrymal region is specially long. This is least marked in the Cereopsis Goose (Cereopsis nova-hollandia), where, however, it is clearly apparent. In Chauna, the lachrymal region is as short as in the Gallinae, not in the least elongated. In both the Anseres and Gallinae the pterygoid bones have large faceted surfaces for articulation with the basisphenoid rostrum. In both groups these facets are situated very far forwards-quite at the anterior ends of the bones in the latter; in Chauna, however, these articulations are quite independent of the anterior ends of the bones (fig. 4), being nearly as far backward as the middle of their otherwise free moieties. As to the quadrate bones, their cranial articulations are bifid, which is the case in all birds except Struthio, Rhea, Dromaus, Casuarius, Apteryx, the Crypturi, and some (most) of the Gallinae. They do to a certain extent resemble the same bones in the Anseres in having the articular surfaces for the jugal arches situated some way behind the level of their mandibular articulations (not a Gallinaceous character), which latter they also resemble in configuration, the usually extended outer facet not running backwards and inwards, as in most birds but not in the Gallinae. In the Gallinae, as in the Crypturi, the pterygo-quadrate articulation is much longer than in other members of the class, In Chauna this is not the case. In Chauna the angle of the mandible is much prolonged and up, curved, as in the Anseres, from which it however differs in not being deepty excavated in the interval between the upturned process and the inwardly-directed articular angle, It must be remembered that the mandible is much the same in the Gallinae. It must also be remembered that the Screamers are the only birds in which there are no uncinate processes to the ribs, as has been shown by Mr. Parker. |