After rotation of the stomach (Fig. 173) the mesogastrium loses its original sagittal direction. It follows the altered position of the original dorsal border of the stomach, which has now become the caudal margin or "greater curvature," by turning caudad and to the left, being at the same time considerably elongated. This occurs during the second month. Hence the dorsal mesogastrium, after leaving the vertebral column, turns ventrad and to the left to reach its gastric attachment along the greater curvature. This is the first indication of the formation of the great omental or epiploic bursa. [Illustration: FIGS. 173-175.--Schema of dorsal mesogastrium after rotation of stomach.] [Illustration: FIG. 173.--Early stage.] [Illustration: FIG. 174.--Later stage, extension of mesogastrium beyond stomach to left, with fundus of blind retrogastric pouch thus created at X.] [Illustration: FIG. 175.--After adhesion over area of dotted line between dorsal mesogastrium and primitive parietal peritoneum. Secondary line of transition from dorsal mesogastrium to parietal peritoneum at X.] The stomach is here considered as developing in situ and as influencing by its growth and change of position the arrangement and direction of the peritoneal layers with which it is connected. As a matter of fact it is well to note that the stomach at first lies above the primitive diaphragm or septum transversum, migrating, however, at an early period into the subhepatic abdominal position. This migration produces a corresponding increase in the length of the oesophagus (Fig. 34) and the stomach, in consequence of this change in position, acquires its ventral and dorsal mesogastrium. For the purpose of explaining the adult peritoneal relations of the organ it is, however, more convenient to regard the stomach as an abdominal organ from the beginning and to deal with the subsequent changes in position from this standpoint. The inaccuracy is slight and renders the comprehension of the succeeding stages easier. It will be noticed (Fig. 173) that the rudimentary retro-gastric space or "lesser peritoneal sac" is bounded ventrally by the dorsal (the primitive _right_) surface of the stomach, while its dorsal boundary is furnished by the ventral (originally _right_) layer of the dorsal mesogastrium. In the primitive condition, therefore, dorsal mesogastrium and stomach form together a straight line sagittal in direction and placed in the median plane of the body. As the result of the developmental changes above outlined this straight line becomes bent at the point where the mesogastrium reaches the stomach (Fig. 173, x). The two component elements of the line (stomach and mesogastrium) hinge on each other here, and the angle which they form opens to the right.