Arteries that carry blood from the gills to various parts of the body are called extrinsic arteries. Four pairs of gills give rise to 4 pairs of external arteries. The first extrinsic artery transports blood to the pseudobranch. From the pseudobranch, blood reaches the eye through the ophthalmic artery. The first and second external bronchial arteries join to form the lateral artery. The carotid artery arises from the tip of the lateral artery. The carotid artery supplies blood to the brain. The external branchial artery arising from the third and fourth gills first joins and then joins the lateral artery. The two lateral arteries join to form the oval arterial ring. It is called Circulus Cephalicus. Dr. Siddiq Publications