Fig. 28-8. The pancreas and portal vein. A, Anterior view showing the head of the pancreas within the cavity of the duodenum. B, Posterior view showing the formation of the portal vein behind the neck of the pancreas. The pancreas develops by the fusion of a dorsal with a ventral component, hence the frequency of two ducts (main and accessory) that open into the duodenum. 1 to 4, parts of the duodenum; G.B., gallbladder. Click for high resolution image.