Development of the calyceal system in the human fetus.

The calyceal system including the papilla, infundibulum, and renal pelvis in human fetuses and neonates was studied histologically and chronologically. There was a considerable discrepancy between the development of the calyceal muscles and the papilla. The protuberant form of the papilla developed much earlier than the calyceal muscle which was observed in the late stage of intrauterine life. The calyceal muscles were differentiated and extended from the renal pelvic muscles through the infundibular muscles after approximately 21 weeks of intrauterine age and were not fully developed by the late stage of intrauterine life. On the other hand, the cup-shaped calyces and the protuberant form of the papilla developed into the form similar to that observed in the adult by the 21st week; their development began in the 16th week. From these observations the etiology of megacalyces was speculated and discussed based on the discrepancy of the muscular development of the calyceal wall and the development of the protuberant papilla.