2. The distal portion of the gland, comprising the body and tail, develops between the layers of the great omentum (dorsal segment), derived from the primitive dorsal mesogastrium.
The transections of the dorsal mesogastrium shown in [Figs. 180] and [181] will now have to be amplified by the introduction of the body of the pancreas between the two layers of the vertebro-splenic segment, in addition to the splenic artery ([Figs. 219] and [220]).
Hence the following facts will be understood:
1. In the adult the splenic artery supplies a series of small branches to the pancreas as it courses along the cephalic border of the gland on its way to the spleen.
2. After the above-described adhesion of the original left leaf of the dorsal mesogastrium (vertebro-splenic segment) to the parietal peritoneum ([Fig. 220]), the dorsal surface of the body of the pancreas loses its peritoneal investment and becomes attached by connective tissue to the ventral surface of the left kidney.
3. The ventral surface of the body of the pancreas is in the adult lined by peritoneum of the “lesser sac”; in other words the organ has practically assumed a “retro-peritoneal” position, its ventral peritoneal covering appearing now as the dorsal parietal peritoneum of the retro-gastric space.
4. When completely developed the extreme end (tail) of the pancreas extends to the left, following the splenic artery, until it touches the mesal aspect of the spleen at the hilus.
5. If we, therefore, leave out of consideration for the moment the transverse colon and duodenum, which will be taken up presently, and confine ourselves to the arrangement of the stomach, pancreas and great omentum, a sagittal section to the left of the median line would result as shown in Fig. 222, after the adult condition of adhesion has been established.
The same process of fixation, which resulted in the anchoring of duodenum and head of pancreas, extends to the body of the gland and the investing omentum. The peritoneum lining the original left, now the dorsal surface of the gland, fuses with the primitive parietal peritoneum covering the diaphragm and the left kidney. The main body of the pancreas in the adult appears prismatic, giving a triangular sagittal section. The dorsal surface is adherent to the ventral surface of the left kidney; the ventral surface is covered by the secondary parietal peritoneum (original right layer of mesogastrium) which lines the dorsal wall of the retrogastric space and omental bursa (lesser peritoneal sac). The great omentum now appears to take its dorsal point of departure along the sharp margin which separates this ventral surface of the pancreas from a third narrower surface directed caudad. This surface, under the conditions which we are at present examining, would be lined by the peritoneum continued onto it from the dorsal layer of the great omentum. This peritoneum merges along the dorsal margin of this caudal surface of the pancreas with the general parietal peritoneum covering the left lumbar region and the caudal part of ventral surface of the left kidney. We have, therefore, along this line a secondary transition from visceral to parietal peritoneum, obtained by the obliteration of the original visceral peritoneum investing the dorsal surface of the pancreas before adhesion to the parietal peritoneum.