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Show 1873.] CAROTID ARTERIES OF BIRDS. 471 In reviewing the above facts, for the purpose of forming an estimate as to the significance in classification of the arrangement of the carotid arteries in birds, the following conclusious m a y be drawn, if the Psittaci be omitted from consideration, which, from the great peculiarities they present among themselves, it will be better to do at present:- 1st. In many cases the uniformity of the carotids is of ordinal importance, all Passeres possessing the left carotid only, whilst both are present in all Columbae, Anseres, Grallae, and Accipitres. 2nd. As a family character, the distribution of the carotids is very suggestive, in some cases presenting a well-marked difference between families otherwise closely allied. For example, the Megapodidee, together with the Cracidae, as Prof. Huxley has so clearly shown*, form a well-established suborder of the Gallinae, and osteologically it is not easy to separate them ; but in the Cracidae both carotids are present, whilst in the Megapodidee the left only is found. The Phcenicopteridae also present a condition peculiar to themselves. In the somewhat ill-defined group, the Coccyges, the carotids give rise to family characters of value. The Bucerotidae and R a m phastidae differ in the latter possessing only a left carotid, whilst the former have both present; and the affinities of the Upupidae m ay be considered nearer to the Ramphastidae, on account of their agreeing with them in this point. The Apterygidae, as well as the Turnicidae and Podicipitidae, are also well distinguished from their allies by their single carotids. 3rd. That Struthio and Rhea must be more than generically distant from one another is indicated by many characters; and the difference in their carotids favours their being placed in separate subfamilies; no such difference tends to divide up the Casuariidae in a similar manner. 4th. Respecting genera, there are none in which the peculiarities of the carotids are not constant in them; but there are some which are separated from others by a difference in the arrangement of these vessels. Cypseloides fumigatus, a Swift, apparently not at all peculiar otherwise, undoubtedly possessed, in the only specimen I have had the opportunity of dissecting, two carotids. That this was an individual peculiarity is extremely improbable, as no similar case has been recorded in any other genus; consequently this genus (or species as it m a y be) differs from all its allies, which only possesss the left carotid. A similar case, resting on similar evidence (a single specimen) is that of Arctica aile, which differs from Alca and Uria, with which its affinities are very close, in having the left carotid only, instead of both. Botaurus, amongst the Ardeidae, has also an arrangement peculiar to itself. As previously remarked, the Psittaci present greater differences among themselves respecting the disposition of the arteries of their necks than all the other orders of birds taken together, one condition being peculiar to them, and the other conditions being all represented amongst them. Without entering into further details * P. Z. S. 1868, p. 298. |
