Medical history records many myths and superstitions surrounding the practice of obstetrics. Each of the past several generations felt that it had made great progress, and we are now advised that "modern" obstetrics is far ahead of the practice of former years. This is no doubt true; yet, there remain many fads and fancies, changing a bit from time to time but still not too far removed from some of the myths and superstitions of bygone times. A careful search of the literature reveals that many of our accepted facts of today are based on the study of an extremely small number of patients. The late Dr. William E. Caldwell made the observation that the long-accepted normal measurements of the female pelvis were based on the measurements of only 50 women. The work of Caldwell and of others, in recent years, has given us the information that the female pelvis