164 THE CAROTID ARTERIES OF BIRDS. 
left was extremely small, and that of the right was nearly the same as 
it would have been if it alone had been present. . ae 
Fig. 5. Fig. 6. 
Fig. 5. Carotids at the base of the neck in the genus Phenicopterus, as found 
by myself in all specimens. 
Fig. 6. Carotids at the base of the neck in Cacatua sulphurea, according to 
Meckel. 
From the list at the end of this paper it is shown that of 300 genera 
in which the arrangement of the carotids has been observed, in 193 of 
them both are present, in 107 the left only ; in one only are both equal 
when they join in the neck; in another they join, the left being the 
smaller; and in one other the right is the smaller under similar con- 
ditions; whilst perhaps one possesses the right only. So it may be 
generally stated that in birds either both carotids are present sepa- 
rate, or the left only exists. Several attempts have been made by 
different authors to account for these peculiarities. According to 
Bauer, the simplicity of the carotids (in other words, the presence of 
the left instead of two) is dependent on the size of the individual, the 
smaller species having the single trunk. Undoubtedly the great 
majority conform to this rule; but there are too many exceptions, as 
shown by Meckel, to make the generalization of much value, Rhea, 
Podiceps, Cacatua, Talegalla, and Menuwra possessing only the left. 
Meckel originally thought that a correlation existed between the 
length of the neck and the simplicity of the carotids; but when he 
found two carotids in Struthio, Dromeus, Cygnus, and Ardea he 
acknowledged that such was not the case. Prof. Owen remarks*, 
“ Birds as a rule are peculiar in sleeping with their long necks much 
bent or twisted; and this position might be expected to exercise some 
effect on the vessels subject thereto. Accordingly we find that the 
* “ Anatomy of Vertebrata,” vol. ii. p. 190. 
