22O THE UROGENITAL SYSTEM 



Transformation of the Miillerian Ducts. The Mullerian, or female 

 ducts, after taking their origin as described on p. 211, grow caudally, 

 following the course of the mesonephric ducts (Fig. 224). At first lateral 

 in position, the Mullerian ducts cross the mesonephric ducts and enter 

 the genital cord median to them (Fig. 238 4)- In embryos of 20 to 30 

 mm. their caudal ends are dorsal to the urogenital sinus, extending as 

 far as the Mullerian tubercle, a projection into the median dorsal wall of 

 the vesico-urethral anlage formed by the earlier entrance of the mesone- 

 phric ducts (Fig. 219). This tubercle marks also the position of the 

 future hymen. In fetuses of 70 mm. (C H) the Mullerian ducts break 

 through the wall of the urethra and open into its cavity. Before this 

 takes place, the caudal ends of the Mullerian ducts, which are pressed 

 close together between the mesonephric ducts in the genital cord, fuse, 

 and in both male and female embryos of 20 to 30 mm. give rise to the 

 unpaired anlage of the uterus and vagina (Figs. 219 and 231 A). The 

 paired cranial portions of the Mullerian ducts become the uterine tubes. 

 During development the ostial ends of the uterine tubes undergo a true 

 descensus from the third thoracic to the fourth lumbar vertebra. 



In the male, these parts are rudimentary. Those portions of the 

 Mullerian ducts corresponding to the uterine tubes and uterus begin to 

 degenerate at 30 mm. The vaginal portions remains as a pouch on the 

 dorsal wall of the urethra, the vagina masculina, or prostatic utricle. 

 The older term, uterus masculinus, is obviously a misnomer which 

 should be abandoned. The extreme cranial end of each Miillerian duct 

 persists as an appendix testis (Fig. 238 C). 



The Uterus and Vagina. -Since the Mullerian ducts develop in the 

 urogenital folds, they make two bends in their course (Fig. 231 A) corres- 

 ponding to those of the folds (p. 209). Each consists of a cranial longitu- 

 dinal portion, a middle transverse portion, and a caudal longitudinal 

 portion which is fused with its fellow to form the 'utero-vaginal anlage. 

 At the angle between the cranial and middle portions is attached the 

 inguinal fold, the future round ligament of the uterus (Figs. 232 and 233). 

 The mesenchyma condenses about the utero-vaginal anlage and the middle 

 transverse portion of the Mullerian ducts, forming a thick, sharply defined 

 layer, from which is differentiated the muscle and connective tissue of the 

 uterus and vagina (Fig. 231 B). As development proceeds, the cranial 

 wall between the transverse portions of the Mullerian ducts bulges out- 

 ward, so that its original cranial concavity becomes convex (Fig. 231 B). 

 The middle, transverse portions of the ducts are thus taken up into the 

 wall of the uterus forming itsfundus, while the narrow cervix of the uterus 

 and the vagina arise from the utero-vaginal anlage. Through the dif- 

 ferentiation of its mesenchymatous wall, the uterus is first brought into 

 relation with the round ligament. 



