Regarding several theories of the evolution of the Sphenisciformes the specific morpho-physiological alterations for the changeover from aerial to underwater life are discussed. The peculiarities in the Penguin's "construction" become comprehensible as strong adjustments to the subaquatic locomotion. Surely they took their origin from the equipment of flying birds. The present data of the kinematics of the underwater locomotion show, that propulsion is produced in the same principal way by the flapping wings as in aerial flight. Therefore the short term "underwater flight" for the Penguin's style of locomotion is justified. Known data of swimming performance suggest that its essential adaptation is not that to top achievements but more to an economical use of energy budget. The favourable hydrodynamic characteristics of the Penguin body may be well interpreted from this point of view. The peculiarity of underwater flight is the absence of the necessity to produce a weight-compensating force. In order to create thrust forces in an appropriate magnitude during up- and downstroke of the beating cycle the upstroke must be powered. The anatomical architecture and the mode of operation of the parts of the muscle system must be adjusted to this demand. Based on these statements, the anatomy of active and passive apparatus of movement was studied by dissection of 26 individuals of Pygoscelis papua, P. antarctica, P. adeliae, Eudyptes chrysolophus, and Aptenodytes forsteri. Besides the functional explanation of the Articulatio sternocoracoidea (diverging considerably from the usual type in birds), a new interpretation is given for the structures of the Articulatio humeri. In this context, the role of the Ligamentum acrocoracohumerale as an important element for coordination of the motion processes in the shoulder joint is elucidated. The essential curvature of the Caput humeri is found to be satisfactorily approximated by a logarithmic spiral. The understanding of the mechanics of bones and tendons leads to a reinterpretation of the role of several groups of muscles which is described in detail. Besides of the preponderant thrust producing (flapping) muscles working mainly in the isotonic manner, muscles can be distinguished which are managing the transfer of the produced forces to the body operating thereby in the isometric way. Another group of muscles has to control the position of the humerus adjusting in this way the hydrodynamic angle of attack corresponding to the respective flow conditions.(ABSTRACT TRUNCATED AT 400 WORDS)