Femur

Definition

In arthropods, the third segment of the leg (counting from the body), located between the trochanter and the tibia. Typically the stoutest segment of the leg, often enlarged and muscular to accommodate the flexor and extensor muscles that control tibial movement. In insects, the femur is usually the longest or most robust leg segment and may bear diagnostic spines, keels, or color patterns used in identification. In spiders and other arachnids, the femur is similarly positioned and may be modified for prey capture (as in raptorial legs) or silk handling. The term derives from the Latin word for thigh, reflecting its functional analogy to the upper leg in vertebrates.

Etymology

From Latin femur ('thigh', 'thigh bone'), applied to arthropod anatomy by analogy to vertebrate limb structure.

Example

In grasshoppers (Orthoptera: Acrididae), the greatly enlarged hind femora house massive extensor muscles that power the characteristic jumping leap; the femoral pattern of light and dark bands is often species-diagnostic.

Related Terms

• Trochanter
• tibia
• Tarsus
• Coxa
• pretarsus
• leg segmentation
• raptorial leg
• saltatorial leg

Usage Notes

Numbering of leg segments varies by convention: some authors count from the body outward (coxa, trochanter, femur...), while others use proximal/distimal terminology. The femur is unambiguously the segment bearing the main tibial flexor muscles. In some groups (e.g., certain Hymenoptera), the trochanter may be fused to the femur, appearing as a single segment; dissection or musculature examination may be required to confirm boundaries. Contrast with 'femur' in vertebrate anatomy, which refers to the single thigh bone—arthropod femora are paired, jointed exoskeletal tubes rather than internal bones.