Term: atrium portion of tissue
Name: atrium
Synonyms:
Definition: Cavitated compound organ that receives inflow of deoxygenated blood and delivers it to a muscular cardiac ventricle. Valves are present to direct flow. There are only two chambers present in the fish heart.
Ontology: Anatomy Ontology [ZFA:0000471]

Name: portion of tissue
Synonyms:
Definition: Anatomical structure, that consists of similar cells and intercellular matrix, aggregated according to genetically determined spatial relationships.
Ontology: Anatomy Ontology [ZFA:0001477]