DEVELOPMENT OF THE UKO-GENITAL OKGANS. 



1335 



deferens from the more caudal portion. The ductuli aberrantes and the rudimentary 

 tubules of the paradidymis are to be looked upon as persistent tubules, of a more caudal 

 portion of the Wolffian body, which have failed to become connected with the tubules of 

 the testis. 



The seminal vesicles are developed in the third month as evaginations which arise from 

 the Wolffian ducts, near their caudal extremities. Each at first has the appearance of a 

 longitudinal groove in the wall of the ductus deferens, which closes over and becomes cut off 

 from the main tube except at the point where, later, the duct of the seminal vesicle joins 

 the ductus deferens. 



The Miillerian ducts atrophy in the male embryo, but the appendices of the testis are 

 vestigial remains of their cephalic portions, while the utriculus prostaticus represents the 

 caudal fused portions which, in the embryo, occupy the genital cord. 



Ducts in the Female. The Mtillerian ducts in the female retain their openings into 

 the body cavity, and their cephalic portions become the uterine tubes. Their fused 

 caudal parts, which at first join the uro-genital canal, give rise to the uterus and 

 vagina. The manner in which the original position of the opening of the Miillerian ducts 

 becomes shifted, by the formation of a new passage or by the shortening of the uro- 

 genital canal, has already been mentioned 

 (p. 1333). The final position of the opening 

 is in the uro-genital cleft of the adult. 



The vaginal portion of the fused 

 Miillerian ducts is at first relatively very 

 short, and at the point where it opens into 

 the uro-genital canal a slight fold appears, 

 which is the future hymen. The vagina 

 increases rapidly in length as its opening 

 moves downwards towards the uro-genital 

 cleft. In the human embryo during the 

 third month the closely applied Miillerian 

 ducts, which higher up have fused to form 

 the uterus, are represented at their inferior 

 ends by a pair of rapidly elongating solid 

 cellular cords, which at a later stage break 

 down to form the vagina. 



The Wolffian ducts and the mesonephros 

 atrophy in the female, but traces of them are 

 to be found in the ep-oophoron and par-ooph- 

 oron of the adult. In the foetus the Wolffian 

 duct can be traced along the side of the 

 uterus as far as the upper end of the vagina. 



Prostate. The glandular portion of 

 the prostate arises as a series of solid out- FIG. 1047. THE URO-GENITAL PASSAGES m THE 



FEMALE. 



Derivations of the Miillerian duct, orange. Ureter, 

 green solid outline. The ep-oophoron is indicated 

 in green near the opening of Miillerian duct and 

 near the ovary. 



growths from the epithelium of the uro- 

 genital canal during the third month. The 

 outgrowths, which are at first simple, be- 

 come branched and finally acquire a lumen. 

 They are arranged in three groups an 

 upper and a lower dorsal, and a ventral group. The glands of the ventral group soon 

 became reduced in number and often completely disappear ; those of the upper dorsal 

 group form the chief part of the gland. 



The prostatic glands arise in both sexes, but in the female, where they are known as 

 para-urethral glands, they are few in number and not densely packed as in the male. The 

 muscular tissue of the prostate is derived from the muscular wall of the urethra. 



The bulbo-urethral glands arise in the third month, and appear to be developed 

 from the epithelium of the uro-genital canal. 



The larger vestibular glands in the female arise as epithelial outgrowths in the 

 same manner as the bulbo-urethral glands. 



EXTERNAL GENITAL ORGANS. 



The external genital organs are developed in the region of the ectodermal cloacal 

 fossa, and those of . the male and female cannot be distinguished from one another in 

 the earlier stages. The fossa at first extends on the ventral aspect of the body almost 



