chorion

Noun

chorion (plural chorions or choria)

1. The protective and nutritive membrane in higher vertebrates that attaches the fetus to the uterus.
   • The allantois fuses with the chorion, forming a small round area, the allentochorion. This region becomes the placenta (Fig. 3).2002, Rovert E. A. Stewart, Barbara E. Stewart, Female Reproductive Systems, entry in Encyclopedia of Marine Mammals, page 425
   • In this illustration, some license is taken, since the amnion is shown as still separate from the chorion; this is done to illustrate the process of apposition of the amniotic sac to the chorion and to accentuate the interposition of the yolk sac between the amnion and the chorion.2006, Ona Marie Faye-Petersen, Debra S. Heller, Vijay V. Joshi, Handbook Of Placental Pathology, page 4
2. The outer case of an insect egg.
   • The chorion has a predominantly lamellar structure, the lamellae being two-dimensional networks of protein fibrils.1994, Klaus Urich, Comparative Animal Biochemistry, page 392
   • Even closely related species may have chorions differing in thickness. In the silkmoths, for example, the chorion of Bombyx is about 25 μm thick while that of Hyalophora is 55 μm thick.1998, R. F. Chapman, The Insects: Structure and Function, page 326
3. The outer membrane of seeds of plants.