Mammal, bovine placenta (Gross, Low)

Structure List Uterus Allantoic sac Amniotic sac Placentoma Fetal cotyledons Fetus Low Magnification View

The outer membrane of the developing placenta is called the chorionic layer. The amnion layer surrounds the fetus and is continuous with the integument of the fetus. The allantoic layer developed as a sac off the end of the fetal bladder which passed through the umbilical cord and ballooned between the amnion and the chorion. These sacs expand and come in contact to form several double layered membranes. A portion of the horn of the uterus has been removed to reveal the placenta and part of the fetus. This placenta consists of an amniotic sac housing the fetus within an allantoic sac which accumulates wastes. It has a cotyledonary form of attachment. Cotyledons are seen on the surface of the chorioallantoic membrane; they attach to the maternal caruncles to provide for gas and nutrient exchange.