(n.) The membrane lining the cavities of the heart.

abomasum anus appendix bay window beerbelly belly blind gut bowels brain breadbasket cecum colon corporation craw crop diaphragm duodenum embonpoint endocardium entrails first stomach foregut giblets gizzard gullet gut guts heart hindgut honeycomb stomach innards inner mechanism insides internals intestine inwards jejunum kidney kishkes large intestine liver liver and lights lung manyplies maw middle midgut midriff midsection omasum paunch perineum pod pot potbelly potgut psalterium pump pusgut pylorus rectum rennet bag reticulum rumen second stomach small intestine spare tire spleen stomach swagbelly third stomach ticker tripes tum-tum tummy underbelly venter ventripotence vermiform appendix viscera vitals works