The fetal membranes consist of the chorion, amnion, yolk sac, and allantois. The chorion has three layers: cytotrophoblastic, chorionic connective tissue, and basement membrane. The chorion lies ...

Cornified scales of reptiles increased their capacity to live in terrestrial environments. The stratum corneum is very thin, with little keratin. Skin is used for gas exchange. Thick keratin layer ...