294 GENERAL ORNITHOLOGY part ii 



cervical vertebrae, in the hypapophysial canal. Birds with this 

 arrangement Garrod calls aves bicarotidince normales (Fig. 90). 2. In 

 most birds the carotid branch of the right innominate being not 

 developed, only the left, of larger size, traverses the hypapophysial 

 canal ; but it bifurcates before reaching the head, thus producing 

 two carotids, distributed as if there had been two all the way up. 

 Such birds are said to have a left carotid, and are termed aves 

 IcBVO-carotidince (Fig. 91). 3. In certain parrots only, with two 

 carotids, the right is as in (1), but the left runs superficially along 

 the neck with the jugular vein and pneumogastric nerve ; such birds 

 are aves bicarotidince ahnormales (Fig. 92). 4. Two carotids, arising 

 normally, unite almost immediately, and the single trunk runs to 

 near the head, just as if there were two as in (1) ; then it bifurcates, 

 as in birds with left carotid only (2). Such birds are termed aves 

 conjundo-carotidince. Special cases of (4) are : in the bittern, the 

 two roots are of nearly equal size (Fig. 93) ; in the flamingo, the 

 left is very small (Fig. 94) ; in a cockatoo, the right is very small 

 (Fig. 95). Parrots display all four of the arrangements; the cases 

 of the bittern and flamingo are unique. The question is thus for 

 nearly all birds narrowed to whether there be two normal carotids 

 (1), or the left only (2). Observations upon three hundred genera 

 show two in one hundred and ninety-three, in one hundred and 

 seven the left only ; but the numerical proportion of Passerine genera 

 makes (2) the most frequent arrangement. There is but one carotid 

 in all Passeres as far as known ; in most Cy])selidce ; in Trogonidce, 

 Meropidce, Upupidce, Rhaviphastidce, some Psittaci, the Turnicidce, 

 Megapodidce, Podicipedidce, Alcidce, Bheidce, Aj^tert/gidce. Thus in 

 Passeres, Columbce, Accipitres, Gh-allce, and Anseres the carotid arrange- 

 ment is an ordinal character, all but the first named of these great 

 groups having two. The character separates most of the families of 

 "Picarian " birds, and also distinguishes the families Phosnicopteridce, 

 Megapodidm, Cracidce, Turnicidce, Podicipedidce, and family groups of 

 the Eatitce-, from among one another. It is apparently only a 

 generic character in Psittaci, and in Cypselidce, Ardeidoi, and Alcidce. 



Eeaching the skull, the carotids burrow in the bone, between 

 the basitemporal plate and the true floor of the skull, and enter the 

 cranial cavity by the " sella turcica " (the original pituitary space) ; 

 their anastomosis furnishes a sort of " circle of Willis." (Figs. 66, 

 69, 70, ic.) 



Both limbs of birds have a prime peculiarity of their arteries as 

 compared with mammals. In the fore limb, the blood supply being 

 chiefly absorbed by the immense pectoral muscles, vessels which in 

 mammals are small axillary branches appear like the main continua- 

 tion of the subclavian trunk, and the brachial arteries are correspond- 

 ingly reduced. In the leg, the main source of supply is the great 



