Fig. 215.—Cephalic segment of primitive mesentery in schematic profile view.

Fig. 216.—Schematic profile view of primitive mesenteries with formation of omentalbursa and developing spleen and pancreas.

Fig. 217.—Sos scrofa fœt., fœtal pig. Portions of thoracic and abdominal viscera hardened insitu. (Columbia University Museum, No. 1449.)

Fig. 218.—Schematic view of primitive mesentery after intestinal rotation and incipientformation of omental bursa from dorsal mesogastrium.

This double relation of the pancreas to the mesoduodenum and to the mesogastrium forming the omental bursa is well seen in fœtal pigs between two and three inches in length (Fig. 217).

The head portion of the pancreas is seen developing between the layers of the mesoduodenum, while the body and tail of the gland, extending to the left, grows between the two dorsal layers of the omentum bursa towards the spleen, which organ is found connected with the left and dorsal extremity of the omental sac derived from the dorsal mesogastrium.

Before the growth of the great omentum is pronounced the continuity of the mesoduodenum and dorsal mesogastrium can be readily appreciated (Fig. 218). But after the redundant growth of the membrane has carried the great omentum further caudad, the stomach and the two omental layers attached to the greater curvature lie in front of the structures included between the two dorsal layers and conceal them from view ([Fig. 177]).

Figs. 219, 220.—Schematic transection of dorsal mesogastrium, pancreas, spleen, and stomach.
Fig. 219.—Before adhesion to primitive parietal peritoneum (arrow indicates the direction in which the adhesion takes place).
Fig. 220.—After adhesion and formation of secondary line of transition between mesogastrium and parietal peritoneum (lieno-renal ligament).

In sagittal sections to the left of the median line (Figs. 221 and 222) the pancreas now appears included between the layers of the great omentum near their point of departure from the vertebral column. (This point is of course identical with the prevertebral attachment of the primitive dorsal mesogastrium from which the omentum is developed.)

Figs. 221, 222.—Schematic sagittal sections through stomach, pancreas, great omentum, andleft kidney.

Fig. 221.—Before adhesion between dorsal and mesogastrium and parietal peritoneum.

 

Fig. 222.—After adhesion.

The foregoing considerations will, therefore, lead to the conclusion that the pancreas presents, in regard to its peritoneal relations, two distinct segments:

1. The portion adjacent to duodenum (head and neck of the gland) is developed between the layers of the mesoduodenum.