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Show 418 PROF. HUXLEY ON THE CLASSIFICATION OF BIRDS. [Apr. 1 1, organs of this kind than their congeners, accompanied by the correlative hot blood. But since we know that the organs of respiration and circulation of a Bat are very different from those of a Bird, it is quite possible that those of a Pterodactyle may have been different, in detail, from either. Having thus arrived at the conclusion that the class Aves, while well enough defined from all existing Reptiles, is nevertheless far more closely connected with the class Reptilia than with any other, I proceed to inquire how Birds may be subdivided into orders, suborders, and families, by characters equalling, or at any rate approaching, in definiteness those which mark out the corresponding groups among Mammals and Reptiles. I propose to divide the class Aves into three orders: the SAU-RUR. E, the RATITAE, and the CARINATAE. I. The SAURURJE (Haeckel) are represented by the solitary fossil Archceopteryx, which seems to have been distinguished from all other birds by the following characters :- 1. The metacarpal bones are well developed, and are not anchylosed together. 2. The caudal vertebrae are both numerous and large, so that the caudal region of the spine is longer than the body, whereas in all other birds it is shorter than the body. The furculum is complete and strong, and the foot extremely passerine in appearance. The forms of the skull and of the sternum are unknown*. II. The RATITE (Merrem), or the Struthious Birds, differ from all others in the combination of the following peculiarities :- 1. The sternum is devoid of a crest, and ossifies only from lateral and paired centres. 2. The long axes of the adjacent parts of the scapula and coracoid are parallel or identicalf. The scapula has no acromial process, nor has the coracoid any clavicular process; at most there are inconspicuous tubercles representing these processes. 3. The posterior ends of the palatines and the anterior ends of the pterygoids are very imperfectly, or not at all, articulated with the basisphenoidal rostrum, being usually separated from it, and supported, by the broad, cleft, hinder end of the vomer. 4. Strong " basipterygoid" processes, arising from the body of the basisphenoid and not from the rostrum, articulate with facets which are situated nearer the posterior than the anterior ends of the inner edges of the pterygoid bones. 5. The upper, or proximal, articular head of the quadrate bone is not divided into two distinct facets. * The " retention of two unguiculate digits on the radial side of the metacarpophalangeal bones modified for the attachment of the primary quill feathers" (Plnlosophical Transactions, 1863, p. 46) is no distinctive character of Archceopteryx both Struthio and Ehea presenting " two unguiculate digits " iu the manus t M y friend Professor Newton informs m e he had already drawn attention to this important point in his Lectures delivered at Cambridge last autumn |
