femur -
A segment of the leg of an insect or arachnid.
Wikipedia
The femur, or thigh bone, is the most proximal (closest to the body) bone of the leg in vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in the rear legs.
OmegaWiki Dictionary
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femur The bone that extends from the pelvis to the knee in the vertebrate tetrapods, including humans.