ARTERIES

the ve els which carry the blood from the heart to the different parts of the body. The walls of a’s consist of three coats; the external, or tunica adventitia, of fibrous ti ue; the middle, or tunica media, of muscular and yellow elastic ti ue, muscular fibres predominating in the larger and elastic fibres in the smaller a’s; and the internal or tunica intima, of endothelial cells. The two chief a’s of the body are the pulmonary a. and the aorta: the pulmonary a. conveys the impure, or venous blood, from the right side of the heart to be purified in the lungs, whil the aorta conveys the purified bloo i from the left side of the heart, to which the blood comes from the lungs, to the ti ues of the body by means of its branches. Smail a’s join, or anastomose, with one another freely; so that, if a large a. is blocked, the circulation can be carried on by the anastomosing branches, except in the case of the ‘end arteries,’ found, e.g., in the brain and the spleen, which do not anastomose with others; and consequently when. one of the ‘end-arteries’ is blocked, the part which it supplies with blood dies.