198 



GENERAL ORNITHOLOGY. 



and arc termed aves Imvo-carotidincc (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 

 pncniuogastric nerve ; such birds are aves hicarotidincc ahnormahs (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 (3). Such birds 

 are termed aves conjuncto-carotidina:. 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 ftjr nearly all birds narrowed to wlietber 

 there be two normal carotids (1), or the left only (2). Observations upon three hundred genera 

 show two m one hundred and ninety-three, in one hundred and seven the left only ; but the 



Fig. 94. 



Figs. 90-95. — Diagrams of carotid arteries of birds: A, root of aorta; a, arch of aorta, to tlie riglit side ; it, left 

 Innominate; W, right innominate; ?s, left subclavian; r.s', right subclavian; /c, left carotid ; re, right carotid. (1) 

 Fig, 90. Aves hicarotidina ntyrmales, with two carotids, both alike. (2) Fig. 91. Aves lwvo-carotidi7imy with left 

 carotid only. (3) Fig. 92. Aves bicarotUJinfc abnormales, certain luirrots, with two carotidB, not alike. (4, D, 6) 

 Aves conjuncto-caroiidlnw, with two carotids, which speedily unite in one. {4) Fig. 9;}, bittern, both alike. (5) 

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



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 Gypselidcc. ; in Trogonidm, Meropidir, 

 TTpupidm, Bhamphastidte, some Psittaci, the Turnicidte, Megapodidm, Podidpedida, Alcidtc, 

 Rheida:, Apterygida'. Thus in Passeres, Golumba:, Accipitres, Gralla;, and Aiiseres, the 

 carotiil arrangement is an ordinal cliaracter, all but the first named of these great groups 

 having two. The character separates most of the families of " Picarian" birds, and also di.s- 

 tinguishes the families Phmnicoi^teridce, Megapodida:, Cracidm, Turnicida:, Podieipcdid(C, and 

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

 ter in Psittaci, and in Cypselidm, Ardeidm and Alcida;. 



Reaching the skull, the carotids burrow in the bono, between tlie basitemporal plate and 

 the true floor of the skull, and enter the cranial cavity by the " sella tni-cica " (the original 

 pituitary space) ; their anastomosis furnishes a sort of " circle of Willis." (Figs. 06, 09, 70, ic.) 



