Prenatal development

Indifferent Penis of Human Embryo: Medical visualization of an embryonic indifferent penis at 7 weeks. The external genitalia of men and women are derived from the same (homologous) tissues. Shown are the genital tubercle (which will become the penis or the clitoris), urogenital groove and sinus (which will become the bladder and urethra, and also forms the vagina and hymen), labioscrotal folds (which will form the scrotum or the labia majora), and anal groove. These indifferent structures form by the end of the 7th week of development, and fully differentiate into male or female by week 12.

Prenatal development is the process in which an embryo and later fetus develops during gestation. Prenatal development starts with fertilization the first stage in embryogenesis which continues in fetal development until birth.

In human pregnancy, prenatal development, also known as antenatal development, is the development of the embryo following fertilization, and continued as fetal development. By the end of the tenth week of gestational age the embryo has acquired its basic form and is referred to as a fetus. The next period is that of fetal development where many organs become fully developed. This fetal period is described both topically (by organ) and chronologically (by time) with major occurrences being listed by gestational age.

In other animals the very early stages of embryogenesis are the same as those in humans. In later stages, development across all taxa of animals and the length of gestation vary.

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