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The sternum or breastbone, in vertebrate anatomy, is a flat bone. In amphibians and reptiles it is normally shaped like a shield, often made of cartilage. It is absent in both turtles and snakes. In birds it is larger, and has large flight muscles attached to it. Only in mammals does the sternum take on the longer form seen in humans.
- Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. p. 188. .