Changes in the peritoneum during the development of the testis, epididymis and ductus deferens in the pig

The development of the peritoneal folds of the testis, epididymis and ductus deferens of the pig prior to testicular descent was studied in 18 to 82 days-old embryos/fetuses. The parietal attachment of the mesonephros, mesonephric and paramesonephric ducts and gubernaculum constituted the urogenital mesentery. This could be divided in a cranial and a caudal part. The first fixed the mesonephros and had a mesogonad as a secondary fold. The second had two branches, one laterally to the umbilical artery belonging to the gubernaculum (Plica gubernacularis) and the medial to the artery contained the meso- and paramesonephric ducts. The mesogonad was related caudally with Plica gubernacularis. The fold of the meso- and paramesonephric ducts could also be divided in two parts. The caudal was a primary component of the urogenital mesentery, while the cranial was first ventral and later lateral to the mesogonad (mesorchium) and appeared as a secondary fold of the urogenital mesentery (cranial part). A vascular fold contributed to separate the suspensory ligament of the testis from the developing mesorchium. The proposed meaning of the terms used might be useful for comparative studies.