or Choroideis in Anatomy, a term applied to several parts of the body, bearing some resemblance to the chorion. The word is formed from ἀγορεύω, chorion, and ἰδεῖν, likeness.

Choroideis is particularly used for the inner membrane which immediately invests the brain; so called as being intermingled with a great number of blood-vessels, like the chorion: but more usually denominated the pia mater, or meninx tenuis.

Plexus or Lacin Choroideis, is a knot of veins and arteries in the anterior ventricle of the brain, woven out of the branches of the carotid.

Choroideis is also applied to the inner and posterior tunic of the eye, immediately under the sclerotica. It is soft, thin, and black; and its inner or concave surface is very smooth and polished. It has its name from its being interperforated with vessels.