SEC. IV 



ANATOMY OF BIRDS 



293 



of one precaval vein, right instead of left aortic arch, and mode of 

 origin of the primary aortic branches. 



The zoological interest of the avian blood-vessels centres in the 

 carotid arteries, which, with the vertebral arteries, supply the neck 

 and head. The carotids may be single or double ; and other details 

 of their disposition correspond well with certain families and orders 

 of birds. They are the first branches of the innominates. In most 



FiGB. 90-95. — Diagrams of carotid arteries of birds : A, root of aorta ; a, arch of aorta, to 

 the right side ; Zi, left innominate ; ri, right innominate ; te, left subclavian ; rs, right sub- 

 clavian ; Ic, left carotid ; re, right carotid. (1) Fig. 90. Aves iicarotidiTue twrmcUes, with two 

 carotids, both alike. (2) Fig. 91. Aves Icevo-carotidincBy with left carotid only. (3) Fig. 92. 

 Aves bica/roHdvruE abnormaleSi certain parrots, with two carotids, not alike. (4, 5, 6) Aves 

 cmifwnetxhcarotidvruz, with two carotids, which speedily unite in one. (4) Fig. 93, bittern, 

 both alike. (5) Fig. 94, flamingo, left very small. (6) Fig. 95, cockatoo, right very small. 

 (Copied by Shnfeldt from Garrod.) 



birds, there is but one carotid, the left ; in a few, one, formed by 

 early union of two ; in many, two, long distinct. The arrangement 

 will be perceived by the diagrams taken from Garrod's admirable 

 paper (P. Z. S., 1873, p. 457). In nearly the words of this author : 

 1. In what may be termed the typical arrangement (though it is not 

 the usual one), two carotids, of equal size or nearly so, run up the 

 front of the neck, converging till they meet in the middle line, 

 and so continue up to the head, on the front of the bodies of the 



