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
Lesional demyelinations of the central nervous system ventricles within the brain. This morphologic appearance was named Dawson's fingers by Charles Lumsden, after the Scottish pathologist James Walker Dawson, who first defined the condition in 1916. "Dawson's fingers" is the name for the lesions around the ventricle-based brain veins of patients with multiple sclerosis. The condition is thought to be the result of inflammation or mechanical damage by blood pressure around long axis of medular veins. Dawson's fingers spread along, and from, large periventricular collecting veins, and are attributed to perivenular inflammation. Lesions far away from these veins are known as Steiner's splashes. Sometimes experimental autoimmune encephalomyelitis has