Development and organization of the pelvic connective tissue in the human fetus.

The developmental changes in the pelvic connective tissue were studied in 200-600 microns sections through the pelves of human fetuses and newborn children, plastinated with an epoxy resin. Three periods are important for the differentiation of the pelvic connective tissue in fetuses. During a first or mesenchymal period (9-12-week-old fetuses), all pelvic regions identical with the so-called pelvic spaces in the adult are filled with loose undifferentiated mesenchyme. Some pelvic organs are covered by a layer of condensed mesenchyme which later constitutes the connective tissue sheath of these organs. During a second or fibrous period (13-20-week-old fetuses), dense connective tissue predominates. It is arranged in circular and semicircular systems covering the rectum, the bladder and the urethra as well as the peritoneal pouches. The arrangement of dense connective tissue is the same in the male and in the female fetus. No ligaments were found within the pelvic cavity apart from the pubovesical and the puboprostatic ligaments. The connective tissue sheaths of the pelvic organs differ from one another. At the level of the pelvic floor only some of them are directly connected with the parietal pelvic fascia. The pelvic spaces are filled by loose connective tissue. During a third or adipose period (21-38-week-old fetuses) adipose tissue develops within the different compartments of the pelvic cavity so that the clear organization found during the second period is abolished.