ON THE ISSUE OF POSSIBLE FURTHER DEVELOPMENTS OF F. YA. DZERZHINSKY’S RESEARCH PROGRAMME ON THE AVIAN JAW APPARATUS
Due to F.Ya. Dzerzhinsky and his scientific school, the avian jaw apparatus has become a traditional and well-studied topic in Russian functional morphology. Based on decades of communication with Dzerzhinsky, the author attempts to critically review his scientific heritage in order to derive the most promising directions for further research. The analysis undertaken shows that the most significant gap in Dzerzhinsky’s methodology lay in underestimating the problem of muscular mass economy in the avian jaw apparatus, in spite of the severe limitations for weight burden in birds. A new model is suggested, which solves the problem of decreasing the excess mass of jaw muscles, based on the presumed difference in the kinematics of bill opening and food-object compression. In the bill opening, the major adductor muscles can keep almost constant lengths, thus acting as inextensible links in the closed kinematic chain of the kinetic skull. The absence of a necessity to change the length with mouth opening allows for these muscles to be short-fibered and hence light-weight, but strong. Only when a food-object is taken in the bill, the bird makes use of the muscular force by means of locking the quadrate-mandible articulation, which leads to a reformation of the kinematic chain when the food-object is being compressed. Further enhancements of the model are achieved by introducing non-parallel lines of action of the pterygoid muscle and jugal bar. With this feature, the avian jaw mechanism gains a profit of completely employing the available forces of the jaw adductor muscles, avoiding special adjustments to every food-object and to every specific case of its capturing. The major elements of the suggested model, which were discovered by Dzerzhinsky himself, gain new significance in the light of the concept of muscular mass economy. Therefore, a general conclusion is inferred on the adaptive significance of the avian cranial kinesis as a means to reduce the mass of the jaw adductor muscles saving their force. In addition to the new model of jaw mechanics, several other promising directions for the development of Dzerzhinsky’s research are suggested, based on an enriched methodological menu. A challenging topic employing CT-scans and numerical simulations is research of aponeurotic structures in the jaw muscles as a way to optimally pack the muscular fibers of required length in the 3D space available between the other head structures.