Question

Right aortic arch is present in?
A. Mammals only
B. Birds only
C. Both reptiles and birds
D. Both birds and mammals

Answer 1

Hint: Right-sided aortic arch is a rarely occurring variant of anatomy. It implies the presence of an aortic arch on the right hand side instead of the left hand side. The aortic arch present on the right side connects with the right half of the fourth arch thus forming the common dorsal aorta behind the heart during the development of a normal embryo.

Complete answer:
During the embryonic development, six aortic arches are formed. However, in birds and adult humans, only three of them are reserved, say, third, fourth and sixth aortic arches are retained. Moreover, in humans these aortic arches are present on the left side while in birds, the aortic arches are found on the right side. This right aortic arch forms the characteristic feature of all the birds. Here, the right systemic arch is represented by a single aortic arch which supplies arteries to the tissues.
Thus, the right option is B.

Note: Both left and right arches are found in the adult reptiles and amphibians. However, in adult mammals only the left arch is found while in adult birds only the right arch is found. In birds, the systemic arch is formed by the fourth right aortic arch and the anterior arteries which are supplying the head region (internal carotid arteries, common carotid, brachiocephalic) gives rise to the blood vessels in the forelimbs (subclavian arteries).