||A pair of HA are connect one to each AA1. They run rostromedially until at the extreme rostro-ventral midline the two vessels merge and then run straight caudally along the ventral midline until they reach the cranial end of the ventral aorta (VA). There, the single HA passes just dorsal to the rostral end of the VA and then immediately splits again into a pair of HA. The paired HA continue caudally just to either side of the ventral midline. The HA provide blood supply to the ventral branchial region and the heart.