caul, a portion of the amnion, or bag of waters, which is sometimes found remaining around the head of a child after birth. The term also is applied occasionally to the serous membrane covering the heart, brain, or intestines. It is derived from the original meaning of a close-fitting woman’s cap, especially one made of network. Many superstitions were attached to the infant caul; it was looked on as a sign of good luck and, when preserved, was kept as a protection against drowning.