Capillaries

in anatomy, fine hair-like tubes or blood vessels that lead from the ends of the arteries to the beginning of the veins. The diameter of a capillary is such as to allow a roll of blood disks or corpuscles to pass freely. They are so numerous, and they form so fine a network in ordinary parts of the body, that some are sure to be pierced by the prick of a pin. See Blood; Circulation