ABSTRACT
The development of intestine can be characterized by the following two traits. First, at the beginning of its development, the intestine is temporarily herniated into the umbilical cord, then reduced into the abdominal cavity, and finally reaches its adult location, rotating along the way. Nevertheless, no time table is yet available as to show, in a precise manner, when the intestine is herniated, when it is reduced, or to what extent the rotation occurs. Secondly, it is known that in the course of intestinal development, the lumen is temporarily obstructed by epithelial proliferation and then undergoes the recanalization. However, it is not yet certain whether there is practically a complete luminal obstruction, even by supposing that there is a complete obstruction, no theory has yet been established to determine the time, location, or the extent of the obstruction, and the time of the recanalization. In this study, 2 ~12 week old human embryos and fetuses have been used which were microdissected under a surgical microscope and were subsequently observed in an ordinary tissue slide. We have obtained the following results. 1. The intestine was first formed at Carnegie stage 5. Together with the folds of the embryos, three parts of the primitive gut were observed for the first time at stage 10. At stage 12, the primitive gut was located on the midline. 2. At stage 15, the intestine rotated to 90 counterclockwise, and at the next stage, it started herniation. There was another 90 counterclockwise rotation at stage 20, and at the beginning of the 9th week, with the rapid reduction into the abdominal cavity, the cecum was located in the proper adult position, and the rotation completed. 3. Although epithelial proliferation was recognizable in the esophagus, duodenum and other parts of the intestine of the developing embryo, we could not find any cases in which the lumen was completely obstructed.