The sternocostal triangle or foramina of Morgagni (sing.: foramen of Morgagni) are small zones lying between the costal

Rib

In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...

 and sternal attachments of the thoracic diaphragm

Thoracic diaphragm

In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...

. Important vessels that pass through these bilateral foramina include the superior epigastric arteries as terminations of the internal thoracic arteries, with accompanying veins and lymphatics.

Also known as sternocostal hiatus or (Larrey's) triangle.