barrier between thoracic and abdominal cavities; stop gastric contents from refluxing into the oesophagus, breathing control

originate from the cervical somites, likely C3-C5[PMID:23586979]

The diaphragm is a skeletal muscle that is responsible for contraction and expansion of the lungs[GO].

uberon

midriff, phren

phrenic

The mammals are characterized by a diaphragm, which separates the thoracic portion of the body cavity from the abdominal region and assists in drawing air into the lungs and forcing it out. Modern reptiles lack a muscular diaphragm and it is reasonable to suppose that the diaphragm developed as a new device that made possible a large degree of oxygen intake for active animals. The change may have taken place during the transition from reptile to mammal (...).[well established][VHOG]

UBERON:0001103

http://purl.obolibrary.org/obo/NCBITaxon_8782

The urochordate epicardium separates digestive organs from the pharynx and heart, but the anus returns to the upper compartment to discharge wastes through an outgoing siphon (Thoracic_diaphragm#Comparative_anatomy_and_evolution), The existence of some membrane separating the pharynx from the stomach can be traced widely among the chordates. Thus amphioxus possesses an atrium by which water exits the pharynx, which has been argued (and disputed) to be homologous to structures in ascidians and hagfishes.[3]