998 



DEVELOPMENT OF THE URINARY AND SEXUAL ORGANS. 



fringes at their upper opening to form the fimbrise (F) , upon which often a hydatid 

 isjsituated (k 1 ). According to Thiersch and Leuckart the two Wolffian and the 

 two Mullerian ducts lie together below in the genital strand. The two Mullerian 

 ducts now unite at their lower extremities (end of the second month) and form 

 in their combined lumen the vagina and the uterus ([/)> while the upper, free 

 portion of each becomes the oviduct (T). It is thus clear that the condition of 

 double uterus and vagina is due to a developmental defect, resulting from a failure 

 in union. The vagina is originally closed by epithelium; arrest of development 

 may result in atresia of the vagina. The Mullerian ducts empty originally into 

 the lowermost posterior portion of the urinary bladder, below the ureters uro- 

 genital sinus (5) ; later this portion of the bladder becomes elongated posteriorly 

 in such a manner that the vagina (the united Mullerian ducts) and the urethra 

 are united only at a point deep down in the vestibule of the vagina. 

 . 'J The vagina and the uterus are first distinctly separated from each other in 

 the fourth month; between the fifth and sixth months the uterus becomes charac- 

 teristically differentiated. The hymen is formed in the fifth month. 



The testicle lies originally in the inguinal region of the abdomen (Fig. 393, 

 V, f) , supported by a fold of peritoneum (mesorchium, m). From the hilus of the 

 testicle there passes through the inguinal canal to the base of the scrotum (accord- 

 ing to C. Weil, only to the root of the penis) a cord, the gubernaculum of Hunter. 

 Atthe same time there is formed independently from the peritoneum, a sheath- 



3. 



FIG. 393 Development of the External Genitalia. / and //: Genital eminence; r, genital groove; s, coccyx; 

 w, cutaneous elevations. IV: P, penis; R, raphe of the penis; S, scrotum. ///: c, clitoris; /, labia minora; 

 L, labia majora; o, anus. V and VI: Descent of the testicle; t, testicle; m, mesorchium; pv, vaginal process 

 of the peritoneum; M, abdominal wall; S, scrotum. (Diagrammatic.) 



like process extending down to the base of the scrotum (pv) . Arrested develop- 

 ment or atrophy of the gubernaculum of Hunter causes the testicle to be drawn 

 down through the inguinal canal into the scrotum. In its passage the testicle 

 takes with it from the superficial or transverse abdominal fascia the tunica vagin- 

 ahs commums as a covering; and with it the muscular fibers carried down 



rom the ascending and transverse oblique form the cremaster muscle. The 

 peritoneal covering of the testicle becomes the double sac of the tunica vaginalis 

 propria; the vaginal process of the peritoneum is obliterated as a rule, and leaves 



rregular vestiges as the vaginal ligament. If this vaginal process, communicating 

 with the peritoneal cavity, remains patulous, a passage is afforded for the develop- 

 ment ot a congenital external inguinal hernia. 



The ovaries also pass somewhat downward. A strand similar to the guber- 

 naculum of Hunter, passing through the inguinal canal, later becomes the muscular 

 I ligament of the uterus. Also in women the peritoneum sends a vaginal 

 process through the inguinal canal (canal of Nuck). Rarely even the ovaries 



Ascend into the labia majora, while, conversely, a retention of the testicles in 

 the abdominal cavity (cryptorchism) must be looked upon as an arrest of develop- 

 ment. 



The external genitalia are at first not to be differentiated in the two sexes 



393- /I. In the fourth week there is a single orifice at the caudal extremity, 



constituting at the same time the anus and the opening of the urachus, thus a 



aca (Fig. 392, 4, A). In the sixth week an elevation appears in front of the 



rig- 393. /, ), the genital eminence, then laterally from the opening 



