Biomechanics of the multisclerite middle coxa in flies (Diptera)

The middle coxa in Calliphora consists of three sclerites. Two rear sclerites are able to rotate relative to the front sclerite about the intracoxal axis (ICA). The turn ahead about ICA puts the leg in a peculiar position with minimal aerodynamic resistance. Sclerites are articulated in a form of complex kinematic chain. Distances between articulations were measured; using them, various configurations of the model coxa were obtained by geometrical synthesis, the turn about ICA was simulated, and the muscle driving the turn ahead was revealed (the hind elevator). The middle leg with the complex coxa in most of Brachycera is specialised for the advanced flight performance.