THE UTERUS AND VAGINA 



221 



The Hymen. At the point where the utero-vaginal anlage breaks 

 through the wall of the urogenital sinus there is present the tubercle of 

 Muller that marks the lower limits of the vagina. The tubercle is com- 

 pressed into a disk, lined internally by the vaginal epithelium, externally 

 by the epithelium of the urogenital sinus, or future vestibule. These 

 layers, with the mesenchyma between them, constitute the hymen, which 

 thus guards the opening into the vagina (Fig. 238 A, B). A circular 

 aperture in the hymen is for a time closed by a knob of epithelial cells, but 

 later when the hymen becomes funnel-shaped the opening is compressed 

 laterally to form a sagittal slit, the ostium vaginae. Muller's tubercle 

 persists in the male as the colliculus seminalis, from the summit of which 

 leads off the prostatic utricle. 



Cervix uteri 



Vagi 



Uterine tube 



B Fundus of uterus 



Round ligament 

 Transverse portion of 

 uterine tube 



^Mesenchyme 

 FIG. 231. Diagrams showing the development of the uterus and vagina (modified after Felix). 



Growth of the Uterus. The uterus shortens one-third soon afters birth and does not 

 fully recoup this loss until the eleventh year. The virginal size is attained by a short 

 period of rapid growth, chiefly before puberty. 



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 fundus of the uterus remains simple; that of the 

 cervix and vagina becomes stratified (38 mm., C R). 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 solid outgrowths of epith- 

 elium form its fornices. The vaginal lumen appears in fetuses of 150 to 200 mm. (C R), 

 arising by the degeneration of the central epithelial cells. 



Anomalies. Many cases of abnormal uterus and vagina occur. The more common 

 anomalies are: (i) Complete duplication of the uterus and vagina due to the failure of the 

 Mullerian ducts to fuse. (2) Uterus bicornis, due to the incomplete fusion of the ducts. 

 Combined with these defects, the lumen of the uterus and vagina may fail, partly or com- 

 pletely, to develop and the vaginal canal may not open to the exterior (imperforate 

 hymen). (3) The body of the uterus may remain flat (uterus planifundus; Fig. 231 A) or 

 may fail to grow to normal size (uterus fetalis and infantalis). (4) Congenital absence" of 

 one or both uterine tubes, or of the uterus or vagina rarely occurs, but may be associated 

 with hermaphroditism of the external genitalia. The hymen is of variable shape and may 

 be imperforate. 



