Double aoic arch is most common vascular ring, caused by abnormal persistence of the distal segment of the RIGHT of 4th aoic arch. On lateral, arches are posterior to esophagus and anterior to trachea. Symptoms (of tracheal compression or difficulty swallowing) may begin at bih. Aoic arches: Aoic arches are sho vessels connecting ventral and dorsal aoae on each side they run within branchial (pharyngeal) arches are based gradually the 4th and 5th week, in 6 pairs in total the first, second and fifth pairs are developmental in perspective and they soon disappear.1. 1st aoic arch: disappears, a small poion persists and forms a piece of the maxillary aery.2. 2nd aoic arch: disappears, small poions of this arch contributes to the hyoid and stapedial aeries. 3. 3rd aoic arch: common carotid and initial segments of internal carotid aery.4. 4th aoic arch: has ultimate fate different on the right and left side on the left.RIGHT, the proximal segment of the right dorsal aoa persists and is incorporated into the R subclan aery whereas the distal segment regresses.LEFT, both the proximal and distal segments are retained and incorporated into the descending arch of the aoa.5. 5th aoic arch - is transient and soon obliterates.6. 6th aoic arch - pulmonary arch - RIGHT arch: the proximal segment is incorporated into the R pulmonary aery; the distal segment regresses. LEFT arch: the proximal segment is incorporated into the L pulmonary aery; the distal segment persists as the ductus aeriosus.Ref: Embryology for Medical Students, By Sudhir Sant, 2nd Edition, Page 133