[The development of the omental bursa].

The development of the omental bursa (lesser sac) was studied in serial sections of hybrid mouse embryos of 9-11 1/2 days. The anlage of the bursa is represented by several indentations on the right side of the mesenterium. Further growth and topographic alterations of the adjoining organs determine the definitive shape of the lesser sac. On the left side, the recessus pneumato-entericus is a transient structure which persists only until the 11th day of gestation. In humans, the anlage of the bursa is almost identical with its origin in mice. The bursa facilitates the separation from the digestive tract of several organs developing in the mesentery.