Entomology definition of Coxal cavity: the opening or space in which the Coxa
articulates; in Coleoptera the cavity is open when the epimera do
not extend to the sternum; closed or entire when the epimera
reach the sternum or join medially as in Rhynchophora; the
cavities are separated when the prosternum extends between them,
confluent when it does not: see acetabulum.