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THE CAROTID ARTERIES OF BIRDS. 177 
families otherwise closely allied. For example, the Megapodide, 
together with the Cracidx, as Professor Huxley has so clearly shown,* 
from a well-established suborder of the Gallinz, and osteologically 
it is not easy to separate them; but in the Cracidz both carotids are 
present, whilst in the Megapodide the left only is found. The 
Phcenicopteride 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 Bucerotidze and Ramphastide 
differ in the latter possessing only a left carotid, whilst the former 
have both present ; and the affinities of the Upupidz may be considered 
nearer to the Ramphastide, on account of their agreeing with them in 
this point. 
The Apterygide, as well as the Turnicide and Podicipide, 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 Casuariide 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 possess the left carotid. _ 
A similar case, resting on similar evidence (a single. specimen) is 
that of Arctica alle, which differs from Alea and Uria, with which 
its affinities are very close, in having the left carotid only, instead of 
both. Botaurus, amongst the Ardeide. has also an arrangement pecu- 
liar 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 
regarding these birds it is impossible to make any generalizations of Page 472. 
importance ; and I will leave the subject for a special paper on the 
order. 
It is not until the different conditions of the carotid vessels are 
* “Proceedings of the Zoological Society,” 1868,"p. 298. 
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