A. B. Emmons 
43 
measure (0 — T) represents the amount to which the birth canal is prolonged 
downward and backward, when the tuberosities are thus narrowed. 
In recapitulating our findings in respect to the outlet it is fair to say, first 
that this is a complicated space, the points of obstruction being on different and 
diverging planes, varying in divergency, thus multiplying the number of elements 
in the problem. Some of these factors I have tried to elucidate, but others, 
iucluding the ischial spines and the variations in size, shape, and malleability of 
the fetal head, must be left for further studies on the living, and for nature's final 
test of labour. 
By means of the " fetal head " scale the points of impingement on the tuber- 
osities have been determined with comparative accuracy on this series of dry bones. 
These points on the tuberosities were found usually to be on the inner lip of the 
tuberosity at a varying distance from the symphysis. This variation was con- 
siderable and depended on three factors, the curve of these bones, their distance 
from each other, and their distance from the sacrum. By this means it was 
also found that some pelves which appeared to have small generally contracted 
outlets were in reality quite passable. 
The ischial spines, though not available here, must be considered as probably 
an important factor in the mechanism of labour at or near the outlet. 
Finally, emphasis is laid on the importance of the space between the tuber- 
osities, and, when this is reduced, on the available space behind, measured by the 
posterior-sagittal diameter. This combination is probably the most accurate 
practical measure to show the significance of the variations of the outlet. 
The separate bones of the pelvis were measured. The length of the innominate 
bone was obtained by means of the graduated measuring board and block, thus 
giving the maximum distance from crest to tuberosity. The width of the ilium was 
measured with the " compas glissiere " from the anterior to the posterior superior 
. .7 n 1 i ■ n , breadth x 100 
spine. An index tor the larger innominate was figured = = — —. — - . Also a 
r 00 height 
_ . . . 7 height (highest innominate) x 100 
relvic index = — - — ; — , . ,. ± — . 
breadth (mter-crests) 
The sacrum owing to its position of importance and to its great variability 
is a most interesting bone. Its shape often modifies markedly the pelvic cavity. 
Its height was taken from the middle of the anterior surface of the promontory 
to the anterior surface of the tip of the sacrum. The maximum breadth was 
taken with the instrument parallel to the anterior surface of the bone. 
„ , • , breadth x 100 
oacral index = ; — ^-j . 
height 
Four "observations" were added. 1. The number of sacral segments. 2. The 
sacral curvature was estimated as "slight," "moderate," or "pronounced." 3. The 
segment noted at which the curve began. 4. False promontories were noted and 
used for the measure where the cavity was involved in the measurement. 
