Sailors greatly valued this piece of, er, womb and would keep a piece with them at all times (if possible - it's somewhat rare) to ensure that they wouldn't die in a watery grave.

Caul (?), n. [OE. calle, kelle, prob. fr. F. cale; cf. Ir. calla a veil.]

1.

A covering of network for the head, worn by women; also, a net.

Spenser.

2. Anat.

The fold of membrane loaded with fat, which covers more or less of the intestines in mammals; the great omentum See Omentum.

The caul serves for warming of the lower belly. Ray.

3.

A part of the amnion, one of the membranes enveloping the fetus, which sometimes is round the head of a child at its birth.

It is deemed lucky to be with a caul or membrane over the face. This caul is esteemed an infallible preservative against drowning . . . According to Chysostom, the midwives frequently sold it for magic uses. Grose.

I was born with a caul, which was advertised for sale, in the newspapers, at the low price of fifteen guineas. Dickens.

© Webster 1913.