DIAPHRAGMATIC hernias may be divided (after Harrington) into two groups: (1) traumatic (including inflammatory necrosis) and (2) nontraumatic. The latter are structural deficiencies, which may be congenital or acquired. They include (1) esophageal hiatus hernia, due to deficiency of the circular muscle bundles of the hiatus; (2) hernia through the foramen of Bochdalek (pleuroperitoneal hiatus), in which the posterolateral portion of the diaphragm, usually on the left side, fails to fuse; (3) congenital absence of the diaphragm—an enlargement of the foregoing—virtually a more extensive congenital defect extending farther posteriorly, and (4) herniation anteriorly through the foramen of Morgagni or Larrey's spaces. These are the two small spaces devoid of muscle, situated anteriorly on either side of the sternum and immediately behind the anterior costal attachment of the diaphragm. They are filled with loose areolar tissues and contain only the superior epigastric artery and lymphatics. Such a hernia has also been