coxae

Coxa (plural coxae) has two primary uses in anatomy. In human anatomy, each coxa is one of the paired hip bones that form the pelvic girdle. Each coxa is derived from the fusion of three bones—the ilium, ischium, and pubis—which coalesce during late adolescence. The coxae articulate with the sacrum at the sacroiliac joints and with the femurs at the acetabula, forming the hip joints. The acetabulum is the socket for the head of the femur. Together, the two coxae support the upper body, transmit weight to the lower limbs, and protect pelvic organs. Prominent landmarks include the iliac crest and anterior superior iliac spine, and the pubic symphysis connects the two sides anteriorly. Pelvic morphology can differ between sexes, reflecting functional demands, such as childbirth in females.

In arthropod anatomy, the coxa is the proximal segment of a leg that connects to the body, typically articulating with the thorax or cephalothorax. It serves as a lever and site of muscle attachment for leg movement. In insects, the leg sequence is usually coxa, trochanter, femur, tibia, and tarsus. In crustaceans and some other arthropods, the coxa likewise forms the first leg segment near the body. The term is widely used across taxa to describe this proximal leg segment and its articulation, which can vary in structure among different groups.