MECHANICS OF THE AVIAN PROPATAGIUM - FLEXION-EXTENSION MECHANISM OF THE AVIAN WING

The supporting elements of the avian propatagium were examined in inta ct birds and as isolated components, using static force-length measure ments, calculated models, and airflow observations. The propatagial su rface supported between Lig. propatagiale (LP) and brachium-antebrachi um is equally resistant to distortion over the range of wing extension used in flight. The lengths LP assumes in flight occur across a nearl y linear, low-stiffness portion of the force-length curve of its exten sible pars elastica. In an artificial airflow, intact wings automatica lly extend; their degree of extension is roughly correlated with the a irflow velocity. Comparisons between geometric models of the wing and the passive force-length properties of LPs suggest that the stress alo ng LP balances the drag forces acting to extend the elbow. The mechani cal properties (stiffness) of the LP vary and appear to be tuned for f light-type characteristics, e.g., changes in wing extension during fli ght and drag. Lig. limitans cubiti and LP combine to limit elbow exten sion at its maximum, a safety device in flight preventing hyperextensi on of the elbow and reduction of the propatagium's cambered flight sur face. Calculations using muscle and ligament lengths suggest that M. d eltoideus, pars propatagialis, via its insertions onto both the propat agial ligaments, controls and coordinates propatagial deployment, lead ing edge tenseness, and elbow/wing extension across the range of wing extensions used in flight. The propatagial ligaments and M. deltoideus , pars propatagialis, along with skeleto-ligamentous elbow/carpus appa ratus, are integral components of the wing's extension control mechani sm. (C) 1995 Wiley-Liss, Inc.