220 



THE UROGENITAL SYSTEM 



Uterus and Vagina. — Since the Miillerian ducts develop in the urogenital 

 folds, they make two bends m their course (Fig. 231 A) corresponding to those 

 of the folds (p. 208). Each consists of a cranial longitudinal 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 MiiUerian ducts, form- 

 ing a thick, sharply defined layer, from which is differentiated the muscle and 

 connective tissue of the uterus and vagina (Fig. 231 B). As development pro- 

 ceeds, the cranial wall between the transverse portions of the MiiUerian ducts 

 bulges outward so that its original cranial concavity becomes convex (Fig. 231 

 B). The middle transverse portions of the ducts are thus taken up into the 



B Fundus of uterus 



Cervix uleri 



Vagina. 



Round ligament 

 Transverse portion of 

 uterine tube 



Mesenchyme 



Fig. 231. — Diagrams showing the development of the uterus and vagina (modified after FeUx). 



wall of the uterus forming its fundus, while the narrow cervix of the uterus and 

 the vagina arise from the utero-vaginal anlage. Through the differentiation of 

 its mesenchymatous wall, the uterus is first brought into relation with the round 

 ligament. 



At 80 mm. (C R) the mucosa and muscularis may be distinguished. The first circular 

 muscle fibers appear in 180 mm. (C R) fetuses, the other muscle layers develop later. The 

 epithelium of the uterine tubes and the tubal portion of the uterus (fundus) remains simple, 

 with cylindrical or cuboidal cells. The tubular fundus glands of the uterus may not appear 

 until near puberty. The vagina is at first without a lumen. From the third to the sixth 

 months of fetal life dorsal and ventral outgrowths of the epithelium form the forn ices of the 

 vagina. The vaginal lumen appears in fetuses of ISO to 200 mm. (C R), arising from the 

 degeneration of the central epithelial cells. The fornices hollow out and form the boundary 

 line between the cervix uteri and the vagina. The epithelial cells of the former become 

 stratified and cylindrical, those of the vagina are of the stratified squamous type (38 mm. 

 C R). 



