Figure 2. External genital differentiation. The development of external genitalia begins with a bipotential anlage which includes genital tubercle, urethral fold, urethral groove, and genital swellings. In a typical 46, XY, androgen secretion from the testes triggers the fusion of urethral folds, allowing the enclosure of the urethral tube. This, together with the cells from the genital swelling, forms the shaft of the penis. Genital swellings fuse in the midline to allow formation of the scrotum and genital Tubercle expands to give rise to the glans penis. Female external genital development is ensured by the absence of testosterone, it is independent of ovarian endocrine activity. Urethral folds and genital swellings remain separate to form the labia minora and majora. Genital tubercle forms the clitoris.