Structure, Movement, and Myography of the Feeding Apparatus of the Mallard (Anas Platyrhynchos L.) a Study in Functional Anatomy
Structure and functioning of the kinetic apparatus of the mallard (Anas platyrhynchos L.), and degrees of freedom in movements and muscle activities of a functioning kinetic apparatus were investigated. Origins and insertions of the relevant muscles (DAVIDS, 1952) and ligaments, the courses of the muscle fibres, the aponeurotic fibres, the ligaments and ligament fibres and the structure of the bony elements and joints as well as their range of movement, are described. Electromyography and cinematography were used to investigate the muscle activities and movements in three functions of the kinetic apparatus: the straining of fine-grained food in water, the pecking of dry coarse-grained food, and drinking. In relatively constant periods of repetitive actions average pictures of the movements and muscle activities were made for straining. For drinking, the shortest scene was taken as a basis for constructing an average picture. The activity of a muscle was quantified relatively by dividing the difference between the minimal and maximal amplitudes in three steps. This method results in average graduated block diagrams, which were prepared for 18 muscles during straining and drinking and combined with the average synchronized movements. These movements concerned the maxilla and the mandible, with reference to the skull and each other, and the distance between the tips of the beak. Straining is described on the basis of an α and a β cycle model and drinking by two other models: the odd and even postphase cycle model. The movements of the quadrate proved to be critical in these models, since these movements determine the position of the fulcrum between the quadrate and the mandible. Five groups of muscles can be distinguished, delivering respectively: 1. power for opening, 2. guiding for opening, 3. 'streamlining' for the transition from opening to closing, 4. power for closing, 5. guiding for closing. The assumption of coupled kinesis proposed by VON KRIPP (1933a) and BOCK ( 1964) is partially applicable here to the first part of opening the beak. The closing system can be loaded by the tension of active skull adductors and unloaded by the effect of the quadrate adductors and of the ventrolateral and ventromedial pterygoid muscles on the position of the fulcrum between mandible and quadrate. This can result in very high acceleration of movement. The same is shown for the opening system, i.e., loading by the depressors and unloading by the effect of depressors and protractors on the position of the fulcrum. The system is double-coupled, which makes very rapid, guidable, and repeated movements possible. The models for drinking indicate that the guiding system can lead to two modes of application of the forces of the power muscles. An attempt is made to specify quantitatively the α model in a first approximation. The results of this quantification improve the qualitative α model. A distinction is made between "guiding" and "power" muscles on the basis of the differences in structure and functioning of the skull adductors and quadrate adductors in the α and β models. The differences between the characteristics of these muscles are indicated and partially explained. To this end, for in vivo active pinnate muscles the length-tension diagram for in vitro tetanically activated muscles of HILL (1953) is modified such that the maximum available total contraction force can be realized in slightly lengthened pinnate muscles. In addition, the conclusion reached by ERNST (1963) concerning the absence of storage of elasticity in tetanically activated pinnate muscles, was modified for in vivo active pinnate muscles such that for a very short time during very fast stretching and motoneuronal activity, elastic energy as such is stored and is very briefly available. When the patterns for straining, pecking, drinking, and remaining plural and singular actions are compared, in a first approximation the realization of these actions requires only a few more basic macrovariations than the 4 models mentioned. It is necessary to quantify these basic macrovariations to obtain an insight into the totality of mechanical kinetic demands made by the functioning of the feeding apparatus.