D. H. DE Souza 
491 
As the obstetric conjugate and the transverse diameter at the brim have to be 
obtained in practice not by direct measurement but by calculation, and as a know- 
ledge of them is important and often necessary, special attention should be paid 
to these two diameters. The highest correlation ('91) exists between the obstetric 
and diagonal conjugates, and this justifies the reliance always placed by the 
obstetrician on the use of the latter to determine the former. The obstetric 
conjugate shows a moderate degree of correlation ("30) with the antero-posterior 
diameter at the outlet, but the coefficient is small between it and each of the other 
diameters, being very low for the transverse diameter ('07) and pubic height ('05). 
The diameters with which the transverse diameter at the brim is most highly 
correlated are the inter-cristal ('61) and inter-spinous ("52). Next in order are 
the antero-posterior at the outlet ("35) and the inter-tuberal ("32). With the 
other diameters the correlation is low. 
In view of the fact that the pubic height forms one side of a triangle, of which 
the obstetric and diagonal conjugates form the other two sides, it is sometimes 
taken into consideration in calculating the obstetric conjugate from the diagonal 
conjugate. Thus, according to Waldeyer*, "in order to obtain the obstetric 
conjugate from the diagonal conjugate 1"75 to 2 cm., on an average, must be 
subtracted, and, the more acute the angle between the diagonal conjugate and 
the symphysis, and the higher the symphysis, the more must be taken away." 
It will be seen, on referring to the table, that the pubic height is not highly 
correlated with any diameter, and that with the obstetric and diagonal conjugates 
the coefficients are '05 and '14 respectively. 
In order to arrive at formulae for finding the diameters it is necessary to use 
the measurements with which they are most closely correlated. The coefficients 
of correlation of the obstetric conjugate and the transverse diameter at the brim 
with the bone measurements were therefore found, to see whether any of them 
would be high enough to be of service. These are now given : 
Obstetric conjugate Transverse 
Right hip— height ... -55 ±-03 -48 ±-04 
„ „ breadth ... -48±-04 -45 + -04 
Left hip— height ... -56±-03 -45 ±-04 
„ „ breadth ... -51±-03 -48f04 
Sacrum— height ... -31 ±-04 -21 ±'04 
breadth ... -37f04 -56f03 
All these measurements are more highly correlated with the obstetric conjugate 
than is any diameter except the diagonal conjugate ('91). With the transverse 
diameter the measurements of the hip bone show higher correlation than do any 
diameters except the inter-cristal ('61) and inter-spinous ('52), and the coefficient 
of correlation of the breadth of the sacrum with this diameter ("56) is exceeded 
only by that of the inter-cristal with it. Of these measurements, however, the 
only one which can easily be made with sufficient accuracy on the living subject 
* Das Becken, p. 49. Bonn, 1899. 
