GENERAL SKETCH OF UTERINE DEVELOPMENT.
No attempt will be made at completeness, and a few schematic drawings only will be introduced to elucidate the text.
Our knowledge of the first development of the human uterus is im perfect The rudiments of the sexual organs appear about the fourth week, and are alike in both sexes.
Some time after the development of the primitive kidneys, Wolffian bodies, and their excretory channels, the Wolffian ducts, there appear at the anterior and median surfaces of these organs the following two struc tures: 1. The sexual glands, intimately related to and developed from part of the Wolffian bodies. It is a question whether they show any differentiation into testicle and ovaries in their earliest stages. 2. The 3Ifillerian or sexual ducts, also derived from the primitive kidneys, and first lying internal to and then behind the Wolffian c,anals.
These structures later become independent. They do not, however, interest us here, and we will confine our attention to the Miillerian or sexual ducts. These latter soon disappear in the male, or rather remain in their rudimentary condition, and form the vesicula prostatica or uterus masculinus; while in the female they form the excretory duct of the ovaries, and form the basis from which tubes, uterus and vagina are de veloped. These Miillerian ducts, far apart above, approach each other below, without uniting. (See Fig. 4.) At first blind sacs, they open later close to one another in a depression of the external surface, into which the intestinal and urinary canals also open, and which is called the cloaca. (See Fig. 5.) Still later this genital c.anal becomes single, and its opening lies in the sinus nrogenitalis. Animal research shows us that even at the time when these sexual canals are composed merely of epithe lial cells the upper part has a lumen, while the lower part is solid, and has been designated the Mfillerian cord.
When the Mfillerian ducts approach each other and beg-in to unite, they do so earlier at a point a little below their middle than either above or below, at the urogenital sinus. Finally, by the end of the second
month the entire lower halves unite, but only externally; the canals are still separated from one another by a partition wall. (See Fig. 6.) By the third month this has also disappeared, and the lower halves of the Miillerian ducts then form a single canal, while the upper halves remain entirely separate. The union of the two tubes, and the disappearance of the partition extends upwards during the third and fourth months, and goes on until the lower two-thirds have united. (See Fig. 7.) Not until the fifth month, when the union is complete, do other im portant changes begin, leading to the formation of the uterus and vagina out of the Mullerian ducts.
The free and non-united upper thirds of the Mfillerian ducts form the oviducts. As the ovaries descend these portions assume a more and more vertical position. At the upper end a simple smooth-edged opening into the abdominal cavity is formed early, which is transformed later into the fimbriated ostium abdominale. At the point where this upper third joins the united lower two-thirds of the ducts, the round ligament is afterwards attached; and this ligament forms an important landmark in our study of the developmental imperfections of the internal genitals.
Of more importance to us are the transformations which later form the uterus out of the middle third. Towards the end of the third month there appears a, ring-formed projection at the place where the middle runs into the lower third of the canal; and this gradually grows inwards, and encroaches upon the lumen of the canal. In the last months of preg nancy this ring undergoes further changes and becomes the portio vagi nalis and the os externum. A little later the internal os is formed in the same way, and then the walls of the canal between the two rings begin to become thicker and folded, and the cervical canal is formed. The fundns uteri is later formed by thickening of the wall between the tubes; the canal is changed into a triangular cavity, and the uterine cavity is formed.