Two sets of erectile structures join to form the penis and the clitoris.
A pair of cylindrically shaped corpora cavernosa, one on each side of the urogenital triangle, are anchored by their proximal ends to the pubic arch. These attached parts are often termed the crura (from the Latin for “legs”) of the clitoris or the penis. The distal ends of the corpora, which are not attached to bone, form the body of the clitoris in women and the dorsal parts of the body of the penis in men.
The second set of erectile tissues surrounds the openings of the urogenital system.
- In women, a pair of erectile structures, termed the bulbs of the vestibule, are situated, one on each side, at the vaginal opening and are firmly anchored to the perineal membrane. Small bands of erectile tissues connect the anterior ends of these bulbs to a single, small, pea-shaped erectile mass, the glans clitoris, which is positioned in the midline at the end of the body of the clitoris and anterior to the opening of the urethra.
- In me, a single large erectile mass, the corpus spongiosum, is the structural equivalent to the bulbs of the vestibule, the glans clitoris, and the interconnecting bands of erectile tissues in women. The corpus spongiosum is anchored at its base to the perineal membrane. Its proximal end, which is not attached, forms the ventral part of the body of the penis and expands over the end of the body of the penis to form the glans penis. This pattern in men results from the absence of a vaginal opening and from the fusion of structures across the midline during embryological development. As the originally paired erectile structures fuse, they enclose the urethral opening and form an additional channel that ultimately becomes most of the penile part of the urethra As a consequence of this fusion and growth in men, the urethra is enclosed by the corpus spongiosum and opens at the end of the penis. This is unlike the situation in women, where the urethra is not enclosed by erectile tissue of the clitoris and opens directly into the vestibule of the perineum.