External Genitalia and Associated Structures

External Genitalia and Associated Structures

A. Fasciae and ligaments

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1. Fundiform ligament of the penis

• Arises from the linea alba and the membranous layer of the superficial fascia of the abdomen.
• Splits into left and right parts, encircles the body of the penis , and blends with the superficial penile fascia.
• Enters the septum of the scrotum.

2. Suspensory ligament of the penis (or the clitoris)

• Arises from the pubic symphysis and the arcuate pubic ligament and inserts into the deep fascia of the penis or into the body of the clitoris.
• Lies deep to the fundiform ligaments.

3. Deep fascia of the penis (Buck's fascia)

• Is a continuation of the deep perineal fascia.
• Is continuous with the fascia covering the external oblique muscle and the rectus sheath.

4. Tunica albuginea

• Is a dense fibrous layer that envelops both the corpora cavernosa and the corpus spongiosum.
• Is very dense around the corpora cavernosa , thereby greatly impeding venous return and resulting in the extreme turgidity of these structures when the erectile tissue becomes engorged with blood.
• Is more elastic around the corpus spongiosum , which, therefore, does not become excessively turgid during erection and permits passage of the ejaculate.

5. Tunica vaginalis

• Is a serous sac of the peritoneum that covers the front and sides of the testis and epididymis.
• Consists of a parietal layer that forms the innermost layer of the scrotum and a visceral layer adherent to the testis and epididymis.

6. Processus vaginalis

• Is a diverticulum of the peritoneum that traverses the inguinal canal, accompanying the round ligament in the female or the testis in its descent into the scrotum and forms the tunica vaginalis in the male.

7. Gubernaculum

• Is a fibrous cord that connects the fetal testis to the floor of the developing scrotum, and its homologues in the female are the ovarian and round ligaments.
• Appears to play a role in testicular descent by pulling the testis down as it migrates.

B. Male external genitalia

1. Scrotum

• Is a cutaneous pouch consisting of thin skin and the underlying dartos , which is continuous with the superficial penile fascia and superficial perineal fascia. The dartos muscle is responsible for wrinkling the scrotal skin, and the cremaster muscle is responsible for elevating the testis.
• Is covered with sparse hairs and has no fat , which is important in maintaining a temperature lower than the rest of the body for sperm production.
• Contains the testis and its covering and the epididymis.
• Is contracted and wrinkled when cold (or sexually stimulated) to increase its thickness and reduce heat loss, bringing the testis into close contact with the body to conserve heat; is relaxed when warm and hence is flaccid and distended to dissipate heat.
• Receives blood from the external pudendal arteries and the posterior scrotal branches of the internal pudendal arteries.
• Is innervated by the anterior scrotal branch of the ilioinguinal nerve , the genital branch of the genitofemoral nerve , the posterior scrotal branch of the perineal branch of the pudendal nerve , and the perineal branch of the posterior femoral cutaneous nerve.

2. Penis

• Consists of three masses of vascular erectile tissue; these are the paired corpora cavernosa and the midline corpus spongiosum, which are bounded by tunica albuginea.
• Consists of a root , which includes two crura and the bulb of the penis; and the body, which contains the single corpus spongiosum and the paired corpora cavernosa.
• Has a head called the glans penis , which is formed by the terminal part of the corpus spongiosum and is covered by a free fold of skin, the prepuce. The frenulum of the prepuce is a median ventral fold passing from the deep surface of the prepuce. The prominent margin
  of the glans penis is the corona , the median slit near the tip of the glans is the external urethral orifice , and the terminal dilated part of the urethra in the glans is the fossa navicularis.
• Preputial glands are small sebaceous glands of the corona, the neck of the glans penis, and the inner surface of the prepuce, which secrete an odoriferous substance, called smegma.

C. Female external genitalia

1. Labia majora

• Are two longitudinal folds of skin that run downward and backward from the mons pubis and are joined anteriorly by the anterior labial commissure.
• Are homologous to the scrotum of the male. Their outer surfaces are covered with pigmented skin, and after puberty, the labia majora are covered with hair.
• Contain the terminations of the round ligaments of the uterus.

2. Labia minora

• Are hairless and contain no fat, unlike the labia majora.
• Are divided into upper (lateral) parts, which, above the clitoris, fuse to form the prepuce of the clitoris , and lower (medial) parts, which fuse below the clitoris to form the frenulum of the clitoris.

3. Vestibule of the vagina (urogenital sinus)

• Is the space or cleft between the labia minora.
• Has the openings for the urethra, the vagina, and the ducts of the greater vestibular glands in its floor.

4. Clitoris

• Is homologous to the penis in the male, consists of erectile tissue , is enlarged as a result of engorgement with blood, and is not perforated by the urethra.
• Consists of two crura, two corpora cavernosa, and a glans but no corpus spongiosum. The glans clitoris is derived from the corpora cavernosa and is covered by a sensitive epithelium.

5. Bulbs of the vestibule

• Are the homologues of the bulb of the penis, a paired mass of erectile tissue on each side of the vaginal orifice.
• Are covered by the bulbospongiosus muscle, and each bulb is connected to the under-surface of the clitoris.

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