labia majora

Embryologically, the labia majora arise from the labioscrotal swellings, which in males fuse to form the scrotum—making these structures homologous (same embryonic origin). This is a classic USMLE Step 1 concept tested in reproductive embryology, often paired with the analogous relationship between the labia minora and the ventral penile shaft skin, and the clitoris and penis (both from the genital tubercle). Anatomically, the labia majora are two longitudinal folds of skin extending from the mons pubis to the perineum, enclosing the labia minora, vestibule, and other vulvar structures. They contain a core of adipose and fibroelastic connective tissue, along with sweat and sebaceous glands, and are covered externally by pigmented, hair-bearing skin, while the inner surface is smooth and hairless. Clinically, the labia majora are relevant in: (1) Vulvar disorders—Bartholin gland cysts/abscesses occur at the posterior labia majora; lichen sclerosis and vulvar dystrophies can affect this region; (2) Vulvar cancer—most commonly squamous cell carcinoma, often arising in the labia majora, associated with HPV infection or chronic vulvar dermatoses; (3) Development anomalies—ambiguous genitalia in disorders of sexual development (e.g., congenital adrenal hyperplasia) can show fused, scrotalized labia majora due to excess androgen exposure in genetic females; (4) Bartholin’s gland location—posterior aspect of labia majora, relevant to abscess formation. Blood supply is from the external and internal pudendal arteries, and innervation is via the ilioinguinal nerve, genital branch of the genitofemoral nerve, and the pudendal nerve (posterior labial branches).