陰毛
陰毛 (pubic hair) 於青春期出現，初為毳毛 (vellus hair)，並局部被終毛 (terminal hair) 所取代。男性的陰毛分布型態與女性不同，但實務上兩者僅為程度上的差異。毛髮與陰毛的分布在男性之間差異甚大。一般而言，腹壁 (abdominal wall)、陰阜 (pubic mound)、鼠蹊部 (groins)、陰囊 (scrotum) 與會陰 (perineum) 多有毛髮，但臀溝 (natal cleft)、肛周皮膚 (perianal skin)、陰莖遠端體部 (distal penile shaft)、包皮 (prepuce) 與龜頭 (glans) 則無毛。
女性的陰毛發育於青春期始於陰阜 (mons pubis) 與大陰唇 (labia majora)。成人型分布呈三角形，位於陰阜並向大陰唇及大腿延伸，通常在 16–17 歲時發育完全。
圖 12-11：男性與女性外生殖器的形成。(A) 外生殖器形成一對陰唇陰囊皺襞 (labioscrotal folds)、一對泌尿生殖皺襞 (urogenital folds) 與一個前方的生殖結節 (genital tubercle)。在此階段，男性與女性的生殖器在形態上無法區別。(B) 在男性，泌尿生殖皺襞 (urogenital folds) 融合，生殖結節 (genital tubercle) 延長，形成陰莖的體部與龜頭 (shaft and glans of the penis)。泌尿生殖皺襞的融合包覆了確定的泌尿生殖竇 (urogenital sinus)，形成大部分的陰莖尿道 (penile urethra)。尿道遠端的一小段區域則由覆蓋龜頭的外胚層 (ectoderm) 內陷形成。陰唇陰囊皺襞 (labioscrotal folds) 則形成陰囊 (scrotum)。From Bunker C. Male Genital Skin Disease. Saunders Ltd./Elsevier 2004.
Fig. 12.11 Formation of the external genitalia in males and females. (A) The external genitalia form a pair of labioscrotal folds, a pair of urogenital folds and an anterior genital tubercle. Male and female genitalia are morphologically indistinguishable at this stage. (B) In males, the urogenital folds fuse and the genital tubercle elongates to form the shaft and glans of the penis. Fusion of the urogenital folds encloses the definite urogenital sinus to form most of the penile urethra. A small region of the distal urethra is formed by the invagination of ectoderms covering the glans. The labioscrotal folds give rise to the scrotum. From Bunker C. Male Genital Skin Disease. Saunders Ltd./Elsevier 2004.
圖 12-12：肛門生殖器乳腺樣腺體 (anogenital mammary-like glands)。(A) 中倍視野，顯示腺體伴局部囊狀擴張 (focal cystic dilatation)；(B) 高倍視野，顯示雙層細胞壁 (double layered cell wall)。局部可見頂泌分化 (apocrine differentiation) 的徵象。By courtesy of D. Kazakov, Charles University Medical Faculty Hospital, Pilsen, Czech Republic.
Fig. 12.12 Anogenital mammary-like glands. (A) Medium-power view showing glands with focal cystic dilatation; (B) high-power view showing a double layered cell wall. Focally, there is a suggestion of apocrine differentiation. By courtesy of D. Kazakov, Charles University Medical Faculty Hospital, Pilsen, Czech Republic.