Page 458. 
162 THE CAROTID ARTERIES OF BIRDS. 
and Nitzsch, and a few others, are incorporated in the general state- 
ments. 
In birds, the aorta, immediately after it has sprung from the heart, 
divides, as stated by Meckel, and contrary to the opinion of Cuvier, 
into two branches, the left innominate and the continuation of the 
main trunk, This latter again almost immediately divides into the 
right innominate and the descending aortic arch. Each innominate, 
after sending off pectoral and subclavian branches, continues to ascend 
a short way; and when near the superior aperture of the thorax it 
divides into the carotid, vertebral, and thyroid branches, except in 
those in which the carotid of one side is deficient. In what may be 
called the typical arrangement, the carotids, equal in size or nearly 
so, run up the front of the neck from the inner side of each thyroid 
Fig. 1.* Fig. 2. 
h. 
Fig. 1. Carotids at the base of the neck in aves bicarotidine normales. 
Fig. 2. Carotids at the base of the neck in aves levo-carotidine. 
gland, converging until they meet in the middle line, at which spot 
they enter the median intermuscular septum, and continue up to the 
head, on the front of the bodies of the remaining cervical vertebra, in 
the hypapophysial canal, covered by the lateral cervical muscular 
masses, and, where they are present, threading the bony arches. 
Birds with this arrangement are said to have two carotids, and may 
be termed aves bicarotidine normales (see Fig. 1). 
* In these diagrams, which represent the main arteries at the root of the neck, 
the following is the explanation of the abbreviations :—A, origin of the aorta at the 
heart; @, arch of the aorta; J.i, left innominate artery; 7.2, right innominate 
artery; 7.s, left subclavian, and 7.s, right subclavian artery; J.c. left carotid, and 
r.c, right carotid artery. 
