Development of the reproductive system
Paramesonephric ducts

Shortly after the formation of the mesonephric ducts, a second pair of ducts is developed; these are the paramesonephric ducts. Each arises on the lateral aspect of the corresponding mesonephric duct as a tubular invagination of the cells lining the abdominal cavity. The orifice of the invagination remains open, and undergoes enlargement and modification to form the distal tubal opening (abdominal ostium) of the fallopian tube. The ducts pass backward lateral to the mesonephric ducts, but toward the posterior end of the embryo they cross to the medial side of these ducts, and thus come to lie side by side between and behind the latter—the four ducts forming what is termed the common genital cord, to distinguish it from the genital cords of the germinal epithelium seen later in this article. The mesonephric ducts end in an epithelial elevation, the sinus tubercle, on the ventral part of the cloaca between the orifices of the mesonephric ducts. At a later stage the sinus tubercle opens in the middle, connecting the paramesonephric ducts with the cloaca.
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