THE CAROTID ARTERIES OF BIRDS. 163 
A second group is peculiar in having the right carotid branch of 
the innominate undeveloped, when the left only traverses the hypapo- 
physial canal, being of large size; it bifurcates shortly before it 
reaches the head, thus producing a vessel on each side, to be dis- 
tributed in the same way as the terminations of the carotids in the 
previous group. Such birds are said to have a left carotid, and may 
be termed aves levo-carotidine (see Fig. 2). 
In a third arrangement, found only in certain Parrots (see Fig. 3), 
the right carotid artery runs in the hypapophysial canal, and the left 
at the side of the neck superficially along with the corresponding 
pneumogastric nerve and jugular vein. Birds with this arrangement Page 459. 
may be termed aves bicarotidine abnormales (see Fig. 3). 
Fig. 3. Fig. 4. 
A 
Fig. 3. Carotids at the base of the neck in aves bicarotidine abnormales. 
Fig. 4. Carotids at the base of the neck in aves conjuncto-carotidine. 
Fourthly, the two carotids, running apparently as usual, directly 
they meet, join and continue as a single trunk till near the head, 
where the single vessel bifurcates, as in birds with a left carotid only. 
These may be termed aves conjuncto-carotidine. In the common 
Bittern, where this condition obtains, the arteries (Fig. 4) are equal 
in size or very nearly so; but in the Flamingo (Fig. 5) the left is ex- 
tremely small, and has been on this account overlooked by previous 
observers, Meckel, Nitzsch, and Owen stating that there is only a Page 460. 
right carotid in Phanicopterus. I have had the opportunity of examin- 
ing two specimens of Pheenicopterus antiquorum and two of P. ruber ; 
and in all of them both carotids were present in the lower part of the 
neck, the right being much the larger and being joined by the left to 
form one trunk at the point in the neck where they first meet, as in 
Botaurus stellaris. Both vessels carried blood; but the calibre of the 
M 2 
