The genital tubercle is sensitive to dihydrotestosterone and rich in 5-alpha-reductase, so that the amount of fetal testosterone present after the second month is a major determinant of phallus size at birth.
12.
The embroyo develops three distinct external genital structures : a genital tubercle; two urogenital folds, one on either side of the tubercle; and two labioscrotal swellings, each bounding one of the urogenital folds.
13.
It is thought diphallia occurs in the fetus between the 23rd and 25th days of gestation when an injury, chemical stress, or malfunctioning homeobox genes hamper proper function of the caudal cell mass of the fetal mesoderm as the urogenital sinus separates from the genital tubercle and rectum to form the penis.
