fetal membrane vs caul

fetal membrane and caul both are nouns.

Word	Noun	Adjective	Verb	Adverb
fetal membrane	Yes	No	No	No
caul	Yes	No	No	No

As nouns, caul is a hyponym of fetal membrane; that is, caul is a word with a more specific, narrower meaning than fetal membrane:

fetal membrane: any membrane that functions for the protection or nourishment or respiration or excretion of a developing fetus
caul: the inner membrane of embryos in higher vertebrates (especially when covering the head at birth)

Other hyponyms of fetal membrane include allantois, embryonic membrane, veil, umbilical, umbilical cord.

fetal membrane (noun)	caul (noun)
any membrane that functions for the protection or nourishment or respiration or excretion of a developing fetus	the inner membrane of embryos in higher vertebrates (especially when covering the head at birth)
	part of the peritoneum attached to the stomach and to the colon and covering the intestines