The Development of the Hymen 93 



Sinus epithelium : thickness of entire layer, 0.073 mm. ; cells, 13 

 microns high, 6 microns broad; protoplasmic mantle about one-third 

 the diameter of the nucleus. Vaginal epithelium : thickness of entire 

 layer, 1.75 mm.; cells, 17-44 microns in diameter; nucleus one-fifth the 

 size of the cell. The great variation in size of the vaginal cells is worthy 

 of special attention. 



Emhrijo 1 {Fig. 1). The vaginal canal in this 18 cm. fetus can be 

 seen extending a distance of about one centimeter from the cervical 

 indentation to the point where it breaks into the vulva. In its upper 

 four-fifths there is no lumen, the central portion being occupied by an 

 irregularly branching trunk of epithelium, four or five cells in diameter. 

 Tn the lowest one-fifth the canal suddenly widens, the mass of epithelial 

 cells becomes much thicker and a lumen is to be seen that is partly filled 

 with desquamated epithelium. Beneath this epithelial layer lies an area 

 of loose connective tissue cells possessing an embryonal character, with 

 only here and there a connective tissue fibre stained pink by the fuchsin. 

 This layer of embryonal cells is several times thicker than the rod of 

 epithelium in the centre. The outer covering of the vaginal cylinder 

 consists of a thin mantle of connective tissue fibres whose red color, 

 when stained with van Gieson, serves to outline it sharply from the sur- 

 rounding structures. 



The point where the vaginal cylinder enters into the urogenital sinus 

 can be folloAved in nineteen sections. The vaginal conus bends ventrally 

 at its point of entrance into the sinus and thereby a fold is formed 

 between its dorsal wall and the sinus. Microscopically this fold can be 

 seen to consist of the following structures from within outwards: 

 (1) vaginal epithelium, (2) vaginal embryonal connective tissue, 

 (3) fully formed connective tissue fibres from the vagina, (4) fully 

 formed connective tissue fibres from the vulva, (5) vulvar or sinus 

 epithelium. This fold is, therefore, of vulvo-vaginal origin. It corre- 

 sponds in shape and position to the hymen. 



Emlryo 2 {Fig. 2). Fetus 18 cms. long. Owing to the poor state 

 of preservation the epithelium is partly cast off and the hematoxylin 

 stain rather diffuse. In general the state of development approximates 

 that described in Embryo 1. A vaginal lumen can be seen, but it seems 

 to be an artifact due to the desquamation of epithelium. There is no 

 proliferative tendency in the vaginal connective tissue. The bulk of the 

 vaginal conus is composed of embryonal connective tissue cells. The 

 growth along the posterior vaginal wall is less marked, so that the fold 



