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FIGURE 3.—Dorsal view of the right shoulder to illustrate the emergence of the supracoracoideus tendon (arrow)
through the triosseal canal to the tuberculum dorsale (external tuberosity) and its favorable angle for humeral
rotation in four birds with different flight characteristics. A, European Starling (Sturnus vulgaris), a representative
passeriform. During upstroke, the angle of retraction becomes more acute, increasing the ability of the tendon
of insertion to rotate the humerus on its longitudinal axis. A sesamoid bone, the Os humeroscapularis, serves
to deflect the tendon to maintain optimality for humeral rotation. B, pigeon (Columba livia), a representative
columbiform specialized for vertical ascent and descent. The ability of this species to take off from a flat surface
is dependent on the supracoracoideus. c, Great Black-backed Gull (Larus marinus Linnaeus), a charadriiform
that soars and uses relatively low amplitude wingbeats during flapping flight. Note the relatively large tuberculum
dorsale. A decreased angle of retraction coupled with a large tuberculum dorsale results in relatively high
torque. D, Atlantic Puffin (Fratercula arctica (Linnaeus)), a charadiiform specialized for wing-propelled diving.
The supracoracoideus in this and other wing-propelled divers is relatively large to rotate the wing under water.
Each scale bar= 1 cm.
All experiments in this study were performed in accordance
with National Institutes of Health guidelines for animal re­
search and were approved by the Institutional Animal Care and
Use Committee of Brown University. We measured the me-