264 The Philippine Journal of Science 1919 
diameter had a compensatory lengthening, so that the index of 
the posterior plane of the pelvic outlet was either normal or larger 
than normal. This confirms the view of Williams, Daniels, and 
others, that a contracted intertuberal diameter does not neces- 
sarily mean a prolonged or operative labor so long as there is a 
corresponding lengthening of the posterior sagittal diameter. 
Williams has stated that a spontaneous labor is exceptional 
with the following measurements (head, average size) : 
Transverse outlet. Posterior sagittal. 
em. cm. 
8.00 7.5 
7.00 8.0 
6.5 8.5 
6.0 9.0 
5.5 10.0 
but that, with these measurements, a safe delivery through the 
accustomed channel may be effected by instrumental means. 
Daniels, however, basing his calculations on the average normal 
measurements reported by Klein—namely, intertuberal diameter, 
11 centimeters; posterior sagittal, 9.95 or 10 (Daniels uses 10 
instead of 9.95)—has established the following rule: That the 
index of the posterior plane of the pelvic outlet in normal cases 
should be 55, as in the following equation: 
Intertuberal diameter (11) x posterior sagittal (10) 
2 
== 55.0 
or 
Intertuberal diameter * & : 
== 55. 
2 
This index, according to Daniels, may be as low as 33.3 and 
no operation needed but perhaps the use of forceps. 
Following the formula of Daniels, we find that in Filipino 
women, the normal index of the posterior plane of the pelvic 
outlet is much lower than what he considers to be normal for 
American women. It is 
11 Xx 8.5 
“== 46.75 or 46.8; 
and an index as low as 31 may end in spontaneous delivery. 
