The Collaborative International Dictionary of English v.0.48:
Crus \Crus\ (kr?s), n.; pl. Crura (kr?"r?). [L., the leg.]
(a) That part of the hind limb between the femur, or thigh,
and the ankle, or tarsus; the shank.
(b) Often applied, especially in the plural, to parts which
are supposed to resemble a pair of legs; as, the crura of
the diaphragm, a pair of muscles attached to it; crura
cerebri, two bundles of nerve fibers in the base of the
brain, connecting the medulla and the forebrain.