[A three-dimensional computerized reconstruction of the rectum, anus and surrounding muscles of the rat fetus at the 20th gestation day]. 
Using fetuses of Wistar/I rats on the 20th gestation day.  We designed a three-dimensional computerized reconstruction of the rectum, anus and the surrounding muscles.  The tissues were fixed in Bouin's solution sagittally sectioned serially were stained with hematoxylin-eosin.  Light microscopic pictures at 40 x magnification were subjected to the analysis using a three-dimensional image processing system, consisting of a drum-scanner, a general purpose computer (Micro VAX II), and a color image processor.  The results showed that this system clearly reconstructed the three-dimensional image of the rectum, anus and the surrounding muscles and suggested the presence of the puborectal muscle sling.