Labia minora and vestibule of vagina
The anterior endings of both labia minora split and form two layers or two portions:
- Lower layer (also called the medial portion) - joins with the same layer of the opposite side and forms the frenulum of the clitoris as it goes below the clitoris and is attached to the glans of the clitoris;
- Upper layer (also known as the lateral portion) - joins with the upper layer from the opposite labium and forms the prepuce (hood) of the clitoris, which overhangs the glans of the clitoris.
The posterior endings of both labia join together and form a skin fold called the frenulum of the labia minora (also called the fourchette of the labia minora).
The labia minora consist of smooth muscle cells, connective tissue (many elastic fibers), and venous plexuses.
They are thinner than the labia majora and do not have hair. Also, in contrast to the labia majora, they do not contain fat.
The labia minora are rich with blood vessels that become engorged during sexual intercourse, and it causes labia minora to become swelled and more sensitive.
The inner surface of the labia minora is covered by a mucous membrane. Between both labia minora is the vestibule of vagina.
Vestibule of vagina
The vestibule of vagina (sometimes called vulvar vestibule) is the area around the vaginal orifice that is enclosed by the labia minora. It starts right under the frenulum of the clitoris and ends at the frenulum of the labia minora.
The junction zone between the labia minora and the vulvar vestibule is known as Hart's line.
The vestibule of the vagina contains two openings (orifices):
- External urethral orifice - outer opening of the urethra, located approximately 1 inch (2 to 3 cm) below the clitoris;
- Vaginal orifice - opening of the vagina, situated immediately posterior to the external urethral opening.
Also, openings of the greater and lesser vestibular glands are found in the vestibule. The first ones are located along the sides of the vaginal orifice, while the second ones are closer to the external urethral orifice.
The vaginal orifice and, therefore, the posterior part of the vulvar vestibule is covered by hymen until the first sexual intercourse. Most females do have it, but not all.
The hymen is a thin fold made by a mucous membrane that partially reduces the size of the vaginal orifice. The shape and size vary, although usually, it has a semilunar or circular shape with smooth edges or circular shape with fringes going into the center. The center of the vaginal orifice usually stays open, although rarely can the hymen cover the vaginal orifice entirely (it is called the imperforate hymen).
Adult females have remnants of the hymen called hymenal caruncles that are small elevations in the mucous membrane around the vaginal orifice.