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| a children's mummer's parade, as on the Fourth of July, with prizes for the best costumes. |
| the offspring of a zebra and a donkey. |
atrium a·tri·um (ā'trē-əm)
n. pl. a·tri·ums or a·tri·a (ā'trē-ə)
A chamber or cavity to which several chambers or passageways are connected.
Either the right or the left upper chamber of the heart that receives blood from the veins and forces it into a ventricle.
That part of the tympanic cavity that lies below the eardrum.
A subdivision of the alveolar duct in the lung from which the alveolar sacs open.
| atrium (ā'trē-əm) Pronunciation Key
Plural atria or atriums A chamber of the heart that receives blood from the veins and forces it by muscular contraction into a ventricle. Mammals, birds, reptiles, and amphibians have two atria; fish have one. |
sing. atrium (ay-tree-uhm)
The two upper chambers in the heart, which receive blood from the veins and push it into the ventricles. (See circulatory system.)
atria
in vertebrates and the higher invertebrates, heart chamber that receives blood into the heart and drives it into a ventricle, or chamber, for pumping blood away from the heart. Fishes have one atrium; amphibians, reptiles, birds, and mammals, two
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