1873.] CAROTID ARTERIES OF BIRDS. 4/1 



In reviewing the above facts, for the purpose of forming an esti- 

 mate as to the significance in classification of the arrangement of the 

 carotid arteries in birds, the following conclusions may 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 Columbse, Anseres, Grallee, 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 Megapodidae 

 together with the Cracidae, as Prof. Huxley has so clearly shown*, 

 form a well-established suborder of the Gallinge, and osteologically 

 it is not easy to separate them ; but in the Cracidse both carotids are 

 present, whilst in the Megapodidse the left only is found. The 

 Phcenicopteridse 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 Bucerotidre and Ram- 

 phastidae differ in the latter possessing only a left carotid, whilst the 

 former have both present ; and the affinities of the Upupidaj may 

 be considered nearer to the Ramphastidaj, on account of their agree- 

 ing with them in this point. 



The Apterygidse, as well as the Turnicidse and Podicipitidse, 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 Casuariidfe 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 indi- 

 vidual peculiarity is extremely improbable, as no similar case has 

 been recorded in any other genus; consequently this genus (or 

 species as it may 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 alle, which differs from Aha and TJria, 

 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 con- 

 dition being peculiar to them, and the other conditions being all 

 represented amongst them. Without entering into further details 



* P. Z. S. 1868, p. 298. 



