What, then, is the function of the m.
radialis? The answer to this question is inherent to the anatomical
architecture of the muscle and its association with the subdermal
collagen fibers in the shark skin. Contraction of the m. radialis pulls
taut the orthogonally arrayed mesh of subdermal collagen fibers
while the isovolumetric nature of muscle causes the m. radialis to
bulge and increase the tension in the skin. The end result is that the
tail is stiffened on the side of m. radialis contraction. Most importantly,
the m. radialis contracts as the tail reaches mid-stroke and
passes behind the body ofthe swimming shark. This pointin the tail
beat is when the tail is moving at its greatest velocity, and therefore
is incurring the greatest drag