The chorioallantoic membrane — also called the chorioallantois or abbreviated to CAM — is a vascular membrane found in eggs of some amniotes, such as birds and reptiles. It is formed by the fusion of the mesodermal layers of two developmental structures: the allantois and the chorion. In mammals, this structure forms the placenta. Chorioalloantoic membranes from developing chicken eggs are routinely used in biological and biomedical research to investigate development, angiogenesis, tumors, chemotherapeutic agents, and to propagate and investigate viruses or helminths.