Giraffe have unusually high heart rates for their size, at 150 beats per minute. When the animal lowers its head the blood rushes down fairly unopposed and a rete mirabile in the upper neck, with its large cross sectional area, prevents excess blood flow to the brain. When it raises again, the blood vessels constrict and direct blood into the brain so the animal does not faint. The jugular veins contain several (most commonly seven) valves to prevent blood flowing back into the head from the inferior vena cava and right atrium while the head is lowered. Conversely, the blood vessels
History of the location of the soul the heart does not need the brain to move. Galen recognized the importance of both the heart and the brain in the proper functioning of a human but saw these as two distinct system governed separately. Therefore there are two souls in combat, the brain representing the logical soul and driving logical being, the heart representing spirited actions of movement and impulse constantly at odds with each other and supplied by different supporting systems. Galen states the "liver is the archai" or the source of the veins and blood of the body and is therefore important in regards to the