Hiatus Hernia

Included loosely in the term hiatus hernia are two different conditions—congenital thoracic stomach and true herniation of the stomach through the œsophageal hiatus. In the past the differentiation between the two has been regarded as fairly simple, those cases with a short, straight œsophagus being classed in the congenital variety, but recent work has shown that the problem is not so straightforward, and that the majority of the cases with a short gullet are really acquired. Indeed, the true congenital type is probably quite rare. The developmental mechanism which causes the congenital type is well known. The diaphragm is formed by a number of elements. The antero-central and antero-lateral parts are formed by the septum transversum and fused ventral mesentery, The septum transversum arises from mesoderm in the upper part of the cervical region, and in the 5-mm. to 6-mm. embryo is opposite the fifth cervical segment, whence it draws its chief innervation. As the embryo grows the septum descends, and in the 7-mm. embryo it has migrated downwards below the pulmonary buds and the anlage of the stomach. In the 11-mm. embryo the stomach, already behind in the race, now follows rapidly. May we leave them for a moment to their contest, and consider the development of the rest of the diaphragm, which is formed by the fusion of the dorsal mesentery with mesoderm derived from the Wolffian body, and subsequently with the posterolateral pleuro-peritoneal folds.