This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
In the early stages of development of the human embryo there arises from the parietal mesothelium on each side a tube known as the Wolffian duct with a collection of tubules known as the Wolffian body. This reaches its full development in the seventh week. On one side of the Wolffian body develops the sexual gland, which later becomes either a testicle or ovary. At the caudate extremity of the Wolffian body develops the kidney by the end of the second month. At this time the bladder is connected by the urachus with the stalk of the allantois. The lower end of the bladder is connected with the extremity of the intestinal tract through a dilatation called the urogenital sinus. The union of the urogenital sinus and intestine forms the cloaca. At the time the Wolffian body is developing there appears alongside of it a tube called the duct of Muller. It atrophies in the male but in the female becomes the Fallopian tube, icterus, and vagina. The ureter is developed and becomes connected with the lower portion of the bladder (Fig. 457).
Fig. 457. - The development of the genital organs.
The Wolffian duct and duct of Muller, until about the third month, empty into the urogenital sinus. Differentiation of the sexes begins about the third month and is well advanced in the fifth. The sexual gland in the male becomes the testicle and passing from its lower end is seen the gubernaculum. In the female it becomes the ovary and the round ligament passes from its lower end. The Wolffian body after performing temporarily the functions of a kidney disappears, leaving sometimes a small cyst attached to the upper part of the epididymis in the male and in the broad ligament-near the ovary in the female, known as the hydatid of Morgagni (stalked hydatid). Its lower portion has as its remains some short closed tubes in the tail of the epididymis known as the paradidymis or organ of Giraldes in the male and the paroophoron of the broad ligament in the female. The Wolffian duct, while forming the vas deferens and part of the epididymis in the male, forms the atrophied paroophoron in the female to the inner side of the ovary.
The parovarium or organ of Rosenmuller is the remains of the middle set of Wolffian tubules and in the male forms the epididymis. In the female it is almost always present as a horizontal tube with shorter tubes connected with it, between the layers of the broad ligament near the ovary. The Wolffian duct may persist as a small tube in the broad ligament close to the uterus and vagina and known as the duct of Gartner. The ducts of Mtiller in the male atrophy and form the sinus pocularis of the prostate. Part of them may persist patulous as the duct of Rathke. In the female they form the Fallopian tubes, uterus, and vagina.
A knowledge of the development of the urogenital tract enables one to understand how many of its congenital deformities and subsequent affections are produced. Extrophy of the bladder, epispadias, hypospadias, and various forms of hermaphroditism result when the walls of the bladder and urethra and external genitals fail to develop in the median line. Should the urachus not close, a fistulous tract leads from the bladder to the umbilicus from which urine discharges. Cysts may also form in its course. Should the partition between the rectum within and the dimple of the anus without not become absorbed there is formed one of the varieties of imperforate anus. In some cases the rectum empties into the urethra or bladder, thus forming a cloaca. Should the testicle become arrested in its descent from the region of the kidney it forms what is known as undescended testicle. It may be arrested within the abdominal cavity, in the inguinal canal, or near the external abdominal ring.
The paroophoron gives rise to cysts which have a tendency to develop between the layers of the broad ligament and are papillomatous inside. The parovarium also gives rise to cysts which likewise tend to burrow between the layers of the broad ligament. Cysts arising from Gartner's duct are sometimes found in the vagina. In the male, cysts arising from the Wolffian duct are: (1) encysted hydrocele of the testicle; and (2) general cystic disease of the testicle. Cysts arising from the persistence in the male of the duct of Muller have also been observed in the prostate and seminal vesicles, but they are exceedingly rare.