(_b_) Changes in the direction and extent of the dorsal mesogastrium. (_c_) Development of the pancreas and spleen in connection with the mesogastrium. A. Changes in the Position of the Stomach. The primitive position of the organ above outlined (p. 41) is changed during the course of further development by a twofold rotation. 1. The primitive vertical position, in which the oesophageal entrance occupies the highest cephalic extremity, while the pyloric opening is at the opposite caudal end, is exchanged for one directed more transversely, approximating the two gastric orifices to the same horizontal level. In human embryos of 13.9 mm. the fundus has already descended, the pylorus moving cephalad and to the right, while the cardia becomes shifted more to the left. At the same time the greater growth and prominence of the convex border or greater curvature becomes marked in comparison with the relatively short extent of the opposite margin or lesser curvature. 2. Coincident with this change in position is a rotation around the vertical axis, by means of which the original left side of the stomach is turned ventrad, becoming the ventral or "anterior" surface, while the original right surface of the organ now looks dorsad toward the vertebral column, becoming the dorsal or "posterior" surface of human anatomy. The oesophageal or cephalic end is placed to the left of the median line, while the caudal or pyloric end is situated on the right side (Figs. 169 and 170). [Illustration: FIGS. 169, 170.--Two front views of the entodermal canal. (Minot, after His.)] [Illustration: FIG. 169.--Embryo Sch. 1 of His.] [Illustration: FIG. 170.--Embryo Sch. 2 of His.] The original ventral border, now the "lesser curvature" or "upper border," looks cephalad and to the right, toward the caudal surface of the liver, while the original dorsal border, as the "greater curvature" or "lower border" is directed in the main caudad and to the left. The prominence of this border is still further increased by the greater development of the stomach to the left of the oesophageal entrance resulting in the formation of the "fundus" or "great cul-de-sac." This rotation of the stomach explains the asymmetrical position of the vagus nerve in the adult, the left side of the embryonic stomach, innervated by the left vagus, becoming the "anterior" surface of adult descriptive anatomy and _vice versa_.