Functional anatomy of the tunica muscularis in the upper human duodenum.

The arrangement of the muscular elements in the upper duodenum were examined. Continuity is found between some of the fiber bundles from the outer and inner layers, forming an extensive helicoidal system of bundles. Some fiber bundles from the external layer penetrate the pancreatic stroma while others are related to the tunica adventitia of the duodenum, hepato-duodenal ligament and wall of the gastroduodenal artery.