Measurements of overall wing morphology were taken from two species of megabat, <i>Rousettus aegyptiacus</i> and <i>Pteropus rodricensis. </i> Differences in wing morphological parameters can largely be attributed to differences in flight behaviour and ecology. The cross-sectional geometry of the arm wing bones suggests adaptations to torsional loading as well as bending, or axial, loading during flight. The mechanical properties of the arm wing bones were also investigated using microhardness and cantilever bending techniques. The results were indicative of a low Young’s modulus, perhaps an adaptation to increase resilience and prevent buckling of the elongated bat wing bones during flight. 2D membranous wing profile models were constructed using these morphological parameters and wind tunnel test were used to measure aerodynamic force production at Re = 50 000. High life coefficients (C_Lmaxabout 2.4) and low <i>L/D </i>ratios (L/D_maxabout 10.4) were consistent with values obtained from previous studies on membranous wings. The lift and drag curves also suggested the occurrence of leading edge separation and turbulent reattachment at high angles of attack. Smoke flow visualisation studies confirmed this phenomenon. They also indicated that the protruding spanwise spar improved performance at low angles of attack, yet began to interfere with the process of leading edge separation and turbulent reattachment at higher angles of attack. This strongly suggests that bats should tend to hold their wings at low angles of attack during glide and do not achieve the high lift coefficients of which they are capable. The interplay between leading edge flap angle, spar depth and chord-wise spar position is significantly important in regulating flow separation and force production during gliding flight in such a difficult flow regime.

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After an initial chapter introducing the orbital region and surveying the literature, Chapter Two addresses the scope of the variation in orbital construction with a comprehensive description of the orbits of placental mammals, order by order. This information is used to score 23 morphological characters from the orbital region in representatives from as many eutherian families as possible. These character states are then plotted on to existing phylogenies of the Eutheria in order to study the evolution of orbital characters throughout the group. This elucidates which characters are more plastic than others, which orbital features are characteristic of particular placental groups, and which species are anomalous within their family or order with regard to the orbit. Chapter Three focuses on the muscles of mastication and the variation in their relative proportions throughout the Eutheria. The nature of the stresses and strains generated by these muscles across the skull, and particularly in the orbital region, is considered using dissection and the split-line technique. Drawing on this information, Chapter Four seeks to characterise the variation in orbital structure in a quantitative fashion. The surface areas of orbital bones along with various cranial dimensions in a wide sample of eutherians are measured using a 3-D digitiser. These data are then subjected to a number of statistical techniques such as principal components analysis, analysis of variance and cluster analysis, in order to assess whether orbital structure can be correlated with arrangement of the jaw closing musculature. Finally, all the evidence is drawn together to see if the construction of the orbit can be used as a predictor of masticatory musculature.

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