.■JiVJ TOMY 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 

 mroM artericff, 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 



Fios. 90-05.— Diagrams of carotid arteries of birds : h, root of aorta ; a, areli of aorta, to 

 the right side ; li, left innominate ; ri, right innominate ; Is, left subclavian ; rs, right sub- 

 clavian ; ?c, left carotid ; re, right carotid. (1) Fig. 90. Aves bicarotidince normales, with two 

 carotids, l)oth alike. (2) Fig. 91. Aves kevo-earotidinre, viith left carotid only. (3) Fig. 92. 

 An-- in.urn/hlincB abnormales, certain parrots, with two carotids, not alike. (4, 5, 0) Aves 

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

 botli alike. (5) Fig. 94, flamingo, left very small. (6) Fig. 95, cockatoo, riglit very small. 

 (Copied by Shufeldt 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 ti/jncal 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 



