198 



GENERAL ORNITHOLOGY.- 



and are termed aves IcBVO-ca/roUdinee (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 bicarotidinee abnormales (fig. 92). i. Two carotids, 

 arising normally, unite almost immediately, and the single track 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 conjwncto-cwroUdinm. 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 



Fig. 92. 



Figs. 90-95. — Diagrams of carotid arteries of birds : ft, root of aorta ; a, arch of aorta, to the riglit side ; U, left 

 innominate ; ri, right innominate ; Is, left suljolavian ; rs, right subclavian ; Ic, left carotid; re, right carotid (1) 

 Pig. 90. Aves bicarotid-iiuB normales, with two carotids, both alike. (2) Fig. 91. Aves Icevo-carotidiTue, with left 

 carotid only. (3) Fig. 92. Aves McaroHdince abnormales, certain parrots, with two carotids, not alike. (4, 5, 6) 

 Aves conjtmcto-carotidime, with two carotids, which speedily unite in one. (4) Fig, 93, bittern, both alike. (B) 

 Fig. 94, flamingo, left very small. (6) Fig. 95, cockatoo, right very small. (Copied by Shufeldt from Garrod.) 



numerical proportion of Passerine genera makes (2) the most frequent aiTangement. There is 

 but one carotid in all Passeres as far as known; in most Cypselidce; in TrogonidcB, Merapida, 

 Upupidts, RhamphasUdcB, some Psittad, the TitrnicidtB, MegapodidiB, PodidpedidiB, Alcidee, 

 Bheidis, ApterygideB. Thus in Passeres, Columbce, Aceipiires, GraUce, and Anseres, the 

 carotid arrangement 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 dis- 

 tinguishes the families Phcenieopteridte, Megapodidce, Craddce, TurniddcB, PodicipedidcB, and 

 family groups of the RaUtce, from among one another. It is apparently only a generic charac- 

 ter in Psittaci, and in CypselidtB, Ardeidce and Aldda. 



Beaching 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 famishes a sort of " circle of Willis.'' (Figs. 66, 69, 70, ic.) 



