I' ve read about babies being born with a "CAUL" what is it?

Sailors would pay lots of money for these as it was said a CAUL owner would never drown.There have been lots of stories to back this up but again what is a caul?I' ve read about babies being born with a "CAUL" what is it?
In childbirth, the caul (or veil) is seen as a shimmery coating of the head and face. The caul is harmless and is easily removed by the doctor, midwife, or person(s) attending the childbirth.c A child born in this way is known as a caulbearer.
Medical sources contradict the popular opinion that a distinction needs to be made in relation to the birth caul and the adhesion of the birth (amniotic) sac to the face or head of a child at birth. In this view, the birth caul is a complete membrane covering the face of the child and the amniotic sac, or amnion, is another completely different kind of membrane that surrounds the child in the womb. The caul cannot be wiped off the child's face but must be carefully peeled off, while the adhesion of the amniotic membrane is simply a residue that sometimes sticks to the face, and is part of the afterbirth material
It is stuff covering the baby's head, I think its the amniotic sac
It's part of the inner membrane which encloses the foetus before birth.
My oldest daughter was born with a caul over her face. It is just the sac. My husband said it made her look like an alien when she was just born! They used to be dried out and taken to sea by sailors - they would pay a fortune for them. When they are dried out they are like paper.