Giraffe On The Loose

The jugular veins also contain several (most commonly seven) valves to minimise blood flowing back into the head and assist it getting to the inferior vena cava and right atrium in the same situation. Conversely, the blood vessels in the lower legs are under great pressure (because of the weight of fluid pressing down on them). In other animals such pressure would force the blood out through the capillary walls; giraffes, however, have a very tight sheath of thick skin over their lower limbs which maintains high extravascular pressure in the same way as a pilot's g-suit.
Lifestyle
While giraffes are usually found in groups, the composition of these groups is more fluid than in other social ungulates. They are a largely transient species with few strong social bonds and aggregations usually disband every few hours, although calving groups can last weeks to months. For research purposes, a "group" has been defined as "a collection of individuals that are less than a kilometre apart and moving in the same general direction." Giraffe groups can range from over 40 individuals to only a few individuals with the latter being more common. Female giraffes associate in groups of a dozen or so members, occasionally including a few younger males. Calves and sub-adults are rarely alone. Giraffe groups with young tend to feed in more open areas, presumably to provide better visibility to detect predators. This may reduce their feeding efficiency.