This document discusses vitelline duct (also called the yolk stalk or omphalomesenteric duct), which is the embryonic structure that connects the midgut of an embryo to the yolk sac. It provides details on the constituents of the vitelline duct including vitelline veins and arteries. Doppler values for the vitelline artery are also presented. The document then discusses arachnoid cysts, including their locations, differential diagnosis depending on location, and fetal MR and ultrasound images of a large arachnoid cyst.