in anatomy. All foetuses are wrapped up in at least two coats or membranes; most of them have a third, called *allantois*, or urinary.

Some, as the dog, cat, hare, &c., have a fourth, which has two blood vessels, viz. a vein and an artery, called *omphalo-mesentericus*, because passing along the string to the navel, and terminating in the mesentery.