Editorial note — Chapter VII · The Blood and Its Circulation.

Note. The heart is not nourished by the blood which passes through it. The muscular substance of the heart itself is supplied with nourishment by two little arteries called the coronary arteries, which start from the aorta just above two of the semilunar valves. The blood is returned to the right auricle (not to either of the venæ cavæ) by the coronary vein. The longest route a portion of blood may take from the moment it leaves the left ventricle to the moment it returns to it, is through the portal circulation. The shortest possible route is through the substance of the heart itself. The mean time which the blood requires to make a complete circuit is about 23 seconds.