Name the structure labelled D

(a) Right common carotid aery(b) Right subclan aery(c) Brachiocephalic trunk(d) Left subclan aery(e) Left common carotid aeryAngiography may be performed using CT, MRI or conventional angiography with a catheter. The catheter can be seen on this image in the aoic arch. Normal variants occur in the great vessels so it is impoant to understand normal anatomy to be able to identify any abnormality. An estimated 65% people have the 'normal' anatomy described in textbooks. The commonest anomaly is seen in 5% where the left veebral aery arises directly from the aoic arch, between the origins of the left common carotid and left subclan aeries.