THE DEVELOPMENT OF THE EXTERNAL FEMALE ITAL ORGANS.
A_ In the virgin they are separated from the vagina by the hymen, and they consist of hymen, meatus urinarius, Cowper's or Bartholin's glands, labia majors and minors, clitoris, and perineum.
In order to understand the occurrence and importance of anomalies of these organs, we must preface their study by a sketch of the normal developmental phases.
The genital organs of the male and of the female are derived from a common stock, and so far as we are able to determine there exists primi tively absolutely no difference between them. Both are derived from the Wolffian bodies, Miiller's ducts, and the genital glands.
In Fig. 32 is represented the Wolffian bodies of a male embryo at the thirty-fifth day. These bodies are rightly designated the primitive kid ney, seeing that its secretion contains urea, and its duct opens into the channel for the urine. The Wolffian bodies develop very early in the life of the embryo, and consist of two large glands, one on each side of the spinal column. They are the largest of the fcetal organs in the early months. They are made up of a number of transverse canals, which open into a lateral duct. On the inner border next to the spine lie the genital glands (ovaries and testicles). Further outward and on the an terior surface of the Wolffian bodies develop the ducts of Muller. Both are hence not far from one another. Later they are separated from the primitive kidney by folds of peritoneum.
The permanent kidneys develop behind and above the Wolffian bodies, and are not concerned in the development of the sexual organs. Their ducts, the ureters, extend from them to the bladder.
The lower part of the urinary apparatus—that is to say, the bladder and the urethra—is formed by the allantois, which is a diverticulum from the embryonic rectum. This organ plays an important part in the formation.of the placenta, in that it carries two arterial branches from the umbilicus to the placenta. Further than this statement we are not concerned with the allantois. The diverticulum is known as the urachus, and later the median ligament of the bladder. It is not possible to fol low the development and inter-communication of the various organs as Henle has done, and we reproduce here his illustrations.
The Wolffian bodies develop as we have stated on each side of the ver tebral column. Towards the centre develop the genital tubercles, and more to the outside and above, over the primitive kidneys, stretch the ducts of Mailer. These latter lie between and in front of the duct of the Wolffian body, and unite below, eventually fusing. The separate primitive kidneys and the united canal of MfiIler's ducts open into the lower portion of the allantois, below the bulging of the bladder, and be come the urethra. The ureters, the ducts of the permanent kidneys, de velop higher up in the wider part of the allantois, which ultimately becomes the bladder. Thus then we have the differentiation between
the urethra and the bladder. Still further, Muller's ducts end in a canal which, from the entrance site to the surface of the body, is as well rectum as gc nital canal or urethra, and is, therefore, called the cloaca, until there occurs union between the rectal, vaginal and vesical walls. The accompanying diagrams (Figs. 34 and 35) show the division of this cloaca. The first diagram shows the allantois springing from the rectal canal, from the side of which the ureter opens. In the second diagram is represented schematically the formation of the rectal, vaginal, vesical walls, as well as the hymen, which is the termination of the recto-vaginal wall. The hymen is indeed nothing else than the result of the growing up of the border of the wall lying between the rectum and the vagina. Dohrn says it exists on account of primitive excess of tissue. The hymen does not arise at the site of the uro-genital sinus, but at the lower part of the vaginal canal, which is formed from the ducts of Muller.
The development of the external genitals is to be sought in the geni tal tubercle. This tubercle appears in the sixth week of the life of the embryo, according to KC,Hiker. It soon splits into two. At the expira tion of two more weeks the development of this tubercle is well advanced. In the middle a partition has arisen between it and the opening of the cloaca. In the third months the cloaca has disappeared as such, and the rectum and vagina have been formed. At the end of the third month differentiation in sex has begun. While in the male the genital tubercle becomes the penis, and the genital furrow the urethra, and the sexual folds behind have formed the scrotum, in the female the furrow grows larger and larger, and eventually divides. These divisions remain open, and are the rudiments of the labia majors and minora. The tubercle itself becomes in the female the clitoris.
The essential difference then between the sexes lies in the fact that in the female the uro-genital sinus is not formed from the genital tubercle, and that the urethra does not open into the separated tubercle, but in the uro-genital sinus. A similar difference exists in regard to the cor pora cavernosa in both sexes. In the male they surround the uro-genital sinus, even as the genital furrow and the genital folds unite posteriorly. In the female they only cover the anterior border. One pair of the corpora unite into the two corpora cavernosa clitoridis under the pubic rami, while the other pair, the corpora cavernosa of the urethra or vestibule, sur round the opening of the uro-genital sinus and lie with their posterior side free and ending at the antero-lateral border of the introitus vaginfe.
Into the anatomy of the external genitals we cannot enter. The essentials have already been stated.