External Form of the Embryo and Developmental Stages

Abstract

Prenatal morphogenesis covers a period starting with fertilization and ending with parturition — expulsion of the fetus from the uterus. At the beginning of this period, the unique genetic system of an individual is established by the union of the male and female germ cells (fertilization). Subsequent development of the fertilized oocyte gives rise to the conceptus: embryo, fetus, newborn, and fetal envelopes. The role of genetic factors and their interactions with environmental factors are largely unknown.