n, pl  -nums  or  -na   :  a compound ventral bone or cartilage that lies in the median central part of the body of most vertebrates above fishes and that in humans is about seven inches (18 centimeters) long, consists in the adult of three parts, and connects with the clavicles and the cartilages of the upper seven pairs of ribs - called also breastbone  .
 
 
 
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