36 A Study of the Variations in the Female Pelvis 
from four legs to the hind two. The pelvis, now become a very important girder 
in the bridge structure, thus came to bear the weight not only of the fore part 
of the body but also of the head, and this head has since increased considerably 
in weight. With this large increase in the weight to be carried by the pelvis 
has come a marked change in the direction in which that weight is applied. 
These three factors, the change in direction, the extra weight, and the shortness 
in time since this change has taken place, would lead us to expect changes of 
form of considerable importance and with them variations, the frequent accom- 
paniment of recent change, in those parts to which this function applies. 
The typical " male " pelvis, free from the function of child-bearing, is built 
strong, high, close-knit, thick-boned, with a small cavity, the type best adapted 
to bearing weight. The typical " female " pelvis is, on the other hand, of lighter 
build, lower, more open, and with a roomy cavity, better adapted to child-bearing. 
The newly-acquired function of weight-bearing, however, tends to mould the 
female pelvis toward the male type, while the child-bearing function resists such 
changes in so far as they tend to interfere with its long-established and most 
vital function of child-bearing. To see how nature arbitrates between these 
opposing forces, in other words how with this change the function of child-bearing 
is preserved, was one of the reasons for selecting certain measurements. I have 
also included those diameters and indices with which to compare various groups 
and races. 
Modern pelvimetry, as employed in obstetrics, regards the "obstetric con- 
jugate," * the shortest distance between promontory and pubic symphysis, as the 
chief factor of pelvic efficiency. Secondary in importance to this diameter and corre- 
lated with it, is the breadth of the pelvic " inlet," as shown by the greatest trans- 
verse diameter. A comparison of these two dimensions indicates roughly the shape 
of this space. Lastly, it has been recently emphasized that the pelvic " outlet " 
is a not infrequent cause of difficulty in labour and, if contracted, its efficiency 
may be gauged by the inter-tuberal diameter correlated with the space posterior 
to it. The more exact estimate of these two spaces, so essential to child-birth, 
and the means of calculating them in the living, are the direct objects of certain 
of the measurements taken. 
Inlet. In life direct mensuration of the " obstetric conjugate" (Diagram I, A — R, 
and Plate II) or the conjugata vera cannot be satisfactorily performed. Calcula- 
tions in life from the " external conjugate," the distance from the tip of the spinous 
process of the last lumbar vertebra behind to the top of the pubic symphysis in 
front, as introduced by Baudeloque (5), though often suggestive are admittedly 
unreliable. We have, however, a much more reliable measure for calculation of 
this vera, which is the oblique or diagonal conjugate (Diagram I, A — P), extending 
from the promontory of the sacrum to the lower border of the symphysis, as 
* The "conjugata vera" of the text-books is taken from the promontory of the sacrum to the top of 
the pubic symphysis and is a variable amount longer than the " obstetric conjugate," consequently I 
prefer this shorter measure though both terms are used synonymously. 
