Variations of aortic arch derivatives in the chick (hatchlings).

The branching patterns of the arteries deriving from the embryonic aortic arches were investigated in 1,046 spontaneous chick hatchlings of White Leghorn. An incomplete ductus arteriosus (Botalli) was found on each side of every case observed. An unusual branching patterns were found in 14 hatchlings and were classifiable into the following 4 (B to E) types. Type A (Normal pattern): The aorta arose from the left ventricle and gave off the left and right brachiocephalic arteries. Each brachiocephalic artery was divided into the common carotid and the subclavian arteries. Type B: The right brachiocephalic artery had a slightly higher origin on the aorta. Type C: The right subclavian artery had a slightly lower origin on the right brachiocephalic artery. Type D: The right brachiocephalic artery was absent and the right subclavian and right common carotid arteries arose directly from the arch of aorta. Type E: The distal end of the right brachiocephalic artery fused with the distal part of the arch of aorta.