596 THE HUMAN EMBRYO. 



the duct of Gaertner, running alongside the Fallopian tube (Fig. 

 249, e), and sometimes extending along the walls of the uterus, 

 or even as far as the vagina. 



3. The External Genital Organs. 



These are practically identical in the two sexes, in the 

 early stages of their development ; the distinction between male 

 and female, as regards the external genital organs, not being 

 evident until about the ninth or tenth week. 



At the end of the fifth week (Fig. 234), the septum dividing 

 the rectum from the urino-genital passage has almost reached 

 the surface, but the two passages apparently open by a single 

 cloacal aperture. Immediately in front of this aperture is a 



FIG. 250. FIG. 251. 



FlG. 250. The external genitalia of a Human Embryo of about the ninth 

 week (probably rather younger). (From Kolliker, after Ecker.) x 2. 



c, genital tubercle, or clitoro-penis. /, groove, continuous with urine-genital passage. 

 hi, labio-scrotal folds, n, umbilical cord, s, coccygeal region. 



FIG. 251. The external genitalia of a Human Embryo of about the tenth 



week. (From Kolliker, after Ecker.) x 2. 



rt, anus, e, genital tubercle, or clitoro-penis. /, genital groove, continuous with 

 urino-geuital aperture. M, labio-scrotal folds, s, coccygeal region. 



small conical projection, sg, the genital tubercle or clitoro-penis. 

 The posterior surface of this tubercle is marked by a longi- 

 tudinal groove, which leads, through the cloacal aperture, into 

 the urino-genital passage ; the lips of the groove are slightly 

 swollen, and are continuous with the lips of the cloacal opening, 

 which form the inner sexual folds. The tip of the genital 

 tubercle is expanded into a small knob, the glans. 



A little later, towards the end of the second month, the 

 septum between the urino-genital passage and the rectum 

 reaches the surface, dividing the cloacal aperture into two 

 separate openings, an anterior or urino-genital (Fig. 25 1,/), 

 and a posterior or anal (Fig. 251, a). 



Up to this time the course of development is practically the 



