Single Umbilical Vein - delivers oxygenated blood from the placenta to the fetus. It has a thick layer of circular smooth muscle unlike adult veins.
Wharton's Jelly - the blood vessels are embedded within a matrix of embryonic mucous connective tissue.
Mostly ground substance (primarily hyaluronic acid and chondroitin sulfate) with a low abundance of collagen or reticular fibers.
Mesenchymal Cells - near the remnant of the allantois are many stellate and spindle-like (fusiform) mesenchymal cells. However, spindle-shaped mesenchymal cells are indistinguishable from resting fibroblasts.