Development of the male external genitalia is dependent upon dihydrotestosterone which is produced by the testes. As the genital tubercle is elongating and growing to form the penis, the urogenital folds which lie on either side of the urogenital membrane begin to move towards each other forming a groove, this is known as the urethral groove. The urogenital folds fuse together on the ventral side of the developing penis, enclosing what will now become the spongy urethra. If the urogenital folds fail to close, hypospadias results.
The tip of the penis, which is now called the glans, then begins to form a cord of ectoderm which grows toward the spongy urethra. This cord is known as the urethral plate and when it canalizes, the end of the urethra (external urethral orifice) is at the tip of the penis.
The foreskin is formed in the twelfth week of development. A septum of ectoderm moves inward around the edges of the penis and then breaks down, leaving a thin layer of skin surrounding the penis. During this time, the penis is also developing its corpus cavernosa and spongiosa from proliferating mesenchyme within the genital tubercle.
The labioscrotal folds also grow towards each other and fuse during development to form the scrotum.
