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Giraffes use their long,
prehensile tongues to extend their reach. Specimen at the National
Museum of Natural History, Washington, DC.Giraffes are famous
for their long necks which allow them to browse on the leaves
of trees, and elongated forelegs (which are much longer than the
hind legs). The bony structure of the neck is essentially unchanged
from that of other mammals: there are no extra vertebrae, but
each of the 7 bones is greatly enlarged. Bone constitutes the
bud-like horns called ossicorns, which are covered with the Giraffe's
skin like the rest of the skull.
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Modifications
to the Giraffe's structure have evolved, particularly to the circulatory
system. A Giraffe's heart, which can weigh up to 24 lb (10 kg),
has to generate around double the normal blood pressure for a
large mammal in order to maintain blood flow to the brain against
gravity. In the upper neck, a complex pressure-regulation system
called the rete mirabile prevents excess blood flow to the brain
when the Giraffe lowers its head to drink. 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 exactly the same way as a pilot's g-suit.
Images 1 Through 8 Are Courtesy of US Fish & Wildlife Service
Images 9 through 24 Are Courtesy Of Scotch Macaskill
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