External genitalia and their male–female homologues !

Topic

External genitalia start out the same in both sexes; DHT turns them male, and without it they develop as female.

Updated 2026-11-01

See it in 3D: Glans penis · Clitoris · Corpora cavernosa · Corpus spongiosum · Spongy urethra · Labia minora · Labia majora · Scrotum · Prostate · Bulbourethral glands · Bartholin glands

What it is

Until week 9 the external genitalia look the same: a genital tubercle, two urogenital folds and two labioscrotal swellings around the urogenital membrane. Dihydrotestosterone lengthens the tubercle, fuses the folds to close the urethra and joins the swellings into the scrotum; without DHT each primordium becomes its female homologue. The homologue table is a fixed exam question and the key to hypospadias and differences of sex development.

Key facts

Weeks 4–5: the genital tubercle and folds appear around the cloacal membrane.
Until week 9 the appearance is indifferent.
Weeks 9–14: masculinization by DHT; by about week 14 the penile urethra is closed.
In females, external differentiation proceeds more slowly, to about week 20.
Androgen exposure after week 12 enlarges the clitoris but no longer fuses the labia.

Step by step

The genital tubercle, urogenital folds and labioscrotal swellings form around the cloacal membrane.
The urorectal septum divides the membrane into urogenital (front) and anal (back) parts.
In males DHT lengthens the tubercle into the phallus.
The urethral plate opens into a groove and the urogenital folds close over it from back to front.
The labioscrotal swellings join in the midline to form the scrotum.
In females the folds stay unfused (labia minora) and the swellings stay apart (labia majora).

Genital homologues: one primordium, two outcomes

Primordium	Male	Female
Indifferent gonad	Testis	Ovary
Genital tubercle	Glans, corpora cavernosa	Glans and corpora of clitoris
Urogenital folds	Ventral penis, spongy urethra	Labia minora
Labioscrotal swellings	Scrotum	Labia majora
Urogenital sinus	Prostate, bulbourethral glands	Skene and Bartholin glands
Erectile tissue of the folds	Corpus spongiosum	Vestibular bulbs

Markers

DHT
SRD5A2
AR
SHH

Clinical notes

Hypospadias: the meatus lies on the ventral side because the urogenital folds did not finish fusing.
Epispadias: meatus on the dorsal side, almost always within the exstrophy–epispadias complex.
Virilization of a 46,XX fetus (congenital adrenal hyperplasia): clitoromegaly and labioscrotal fusion.
5α-reductase deficiency or androgen insensitivity in a 46,XY fetus: atypical or female external genitalia.
Empty, separate labioscrotal folds with proximal hypospadias point to evaluation for a difference of sex development.

Test yourself

Think of the answer, then tap the question to see it.

What is the female homologue of the scrotum?

The labia majora; both come from the labioscrotal swellings.

Which primordium forms the labia minora, and what does it form in males?

The urogenital folds; in males they fuse to form the ventral penis with the spongy urethra.

Which hormone masculinizes the external genitalia, and which enzyme makes it?

Dihydrotestosterone, made from testosterone by 5α-reductase type 2.

What is the female homologue of the corpus spongiosum?

The vestibular bulbs.

Which embryological failure causes hypospadias?

Incomplete fusion of the urogenital folds on the ventral side, leaving the urethral meatus short of the glans tip.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Embryology, Urethral Folds - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2023); Embryology, Sexual Development - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2023).

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Representative model, for educational purposes only.