And the keel-like protrusion on their sternums, where the flight muscles attach, shrinks or disappears, except in penguins, who repurpose their flight muscles and keels for swimming.

它们胸骨上龙骨（飞行肌肉附着地方）会收缩或，企鹅除外，它们将飞行肌肉和龙骨重新用于游泳。