42 
A Study of the Variations in the Female Pelvis 
The following table gives the figures of the outlet in convenient condensed 
form : — 
Arch 
(pubic) 
Anteroposterior 
6< 
Inter- tuberal 
Freq. 
Posterior-sagittal 
Freq. 
Roomy 
71 
9- 9'9 cms. 
3 
8- 8-9 cms. 
40 
6-6-9 cms. 
42 
Medium- 
roomy 
4 
10-10-9 „ 
48 
9- 9-9 „ 
73 
7- 7-9 „ 
102 
Medium 
92 
11-11-9 „ 
89 
10-10-9 „ 
85 
8- 8-9 „ 
62 
Medium- 
narrow 
5 
12-12-9 „ 
58 
11-11-9 
16 
9- 9-9 „ 
9 
Narrow 
44 
13-14-66 „ 
19 
12-12-75 „ 
3 
10-11-7 „ 
2 
Average ll - 59cms. 
Maximum 14-66 „ 
Minimum 9 ,, 
9-79 cms. 
12-75 „ 
8 
7-56 cms. 
11-7 „ 
6 „ 
Small outlets, specimens in which the " fetal head " scale measured 9*5 to 
9 cms. in diameter, numbered twenty. As may be seen in the diagrams, the 
backward movement of the tip of the sacrum to the normal amount would 
enlarge these outlets sufficiently to allow the easy passage of the average fetal 
head*, and can thus be considered efficient pelvic outlets. 
The ischial spines, commonly the point of narrowest diameter passed by the 
fetal head in its descent through a normal pelvis, may well be an important factor 
in the mechanism of labour. In my series the attempt was at first made to 
measure this diameter, but in so many specimens it was found that this prominence 
was broken off in part or entirely, that anything like accuracy was impossible. It 
was decided, therefore, that any figures so obtained would be deceiving rather 
than helpful, and none are given. 
An index of the pelvic outlet was estimated as follows : — 
~ , , T , inter-tuberal diameter x 100 
Outlet Index = : ? J , 
antero-posterior of outlet 
average 84-26, maximum 108'9, minimum 64. 
The two diameters used in this index, however, lie in different planes, and can, 
therefore, hardly be considered a true measure of this irregular exit space 
(cf. Plate VI, 7 and Diagram I, 8 — P and S — T). The distance between these 
two diverging planes was estimated at the point opposite the tuberosities by erecting 
a perpendicular (0 — T) with the antero-posterior diameter (P — 8), as a base line, 
to the inter- tuberosities line (T). The distance from the pubes along the base line 
to this perpendicular was also measured to show how far back the tuberosities 
were placed (Diagram I, P — 0). The last of these distances (P — 0) shows approxi- 
mately how far posterior to the pubes the broadest part of the fetal head may 
be forced to pass, when the tuberosities are sufficiently narrowed. The first 
Biparietal diameter 9| cms., sub-occipito-bregmatic 9i cms., Farabeuf and Vernier. 
