The recognition of contraction of the pelvic outlet is almost as old as the recognition of the contracted inlet. Williams1 cites reports by Deventer, de la Motte, and Smellie of isolated cases of outlet contractions. Breisky,2 in 1870 recommended the examination of the intertuberous diameter and invented a pelvimeter to measure it. Klien3 measured the posterior sagittal diameter of the outlet and made the statement that if the intertuberous diameter were 8.5 cm., it would be necessary for the posterior sagittal diameter to be 7 cm. Williams4 and Thorns5 popularized the sum of the intertuberous and the posterior sagittal diameters in this country in the first and second decades of the present century. They recommended 15 cm. as a borderline sum, expecting little difficulty above 15 cm. and increasing difficulty below it.
These two measurements of the outlet, the intertuberous and the posterior sagittal