498 
The Measurements of the Pelvis 
diameters and the height of the left hip bone, shows similar improvement as 
compared with (s), from the inter-cristal diameter and height of left hip bone 
("381 and '380 respectively); while (o), from the inter-cristal, inter-spinous, and 
anteroposterior diameters, has the lowest probable error, '374. 
The best formula then for finding the transverse diameter from a single 
diameter is (k), from the inter-cristal diameter. For two measurements, (r) 
and (s), from the inter-cristal diameter with the height of the right and left 
hip bones respectively, are slightly better than (n), from the inter-cristal and 
inter-spinous diameters, and any of these can conveniently be used as all the 
measurements are easily taken. In the combination of the inter-cristal and 
inter-spinous diameters with a third measurement, the antero-posterior diameter 
gives a better equation (o) than the height of the hip bone, (v) and (w), but the 
measurement of the latter is less objectionable to the patient. 
These formulae were tested in the same way as those for the obstetric con- 
jugate. The transverse diameter was calculated from the recorded measurements 
of 25 of the 216 pelves, picked out at random. The square root of the mean 
square deviation of the calculated from the recorded values of the transverse 
diameter was multiplied by "67449 and compared with the probable errors of 
the equations. In every case they fell within this probable error. 
The formulae were also tested for the five pelves measured by us (I and II 
Egyptian female, III Egyptian male, IV English female, V English male). The 
differences of the calculated from the recorded values for these are given below 
for each equation. 
TABLE V. 
Pelvis Number... 
I 
II 
III 
IV 
V 
Equation 
(*) ... 
- -58 
- 1 -04 
-1-18 
-•27 
-1-57 
11 
(1) ... 
- -99 
- -87 
-1-58 
+ •17 
-1-48 
)! 
(m) ... 
(») ... 
-1-30 
-113 
- "21 
+ •31 
-1-08 
)) 
1) 
- -33 
- -74 
-1-06 
+ •08 
-1-30 
(o) ... 
- -51 
- -93 
-1-16 
+ •09 
-1-40 
11 
(P) - 
-1-00 
- -86 
- -86 
- -04 
-2-12 
11 
(?) - 
-1-09 
- -83 
- "83 
+ -05 
-2-10 
11 
(r) ... 
- -51 
- "90 
- 1 "22 
-•20 
-1-86 
11 
0 .» 
- "54 
- "91 
-1-22 
- -18 
-1-81 
11 
(0 ... 
- -74 
- "77 
- 1"56 
+ •15 
-1-95 
11 
(u) ... 
- -81 
- -77 
-1-45 
+ •20 
- 1-90 
11 
(«) - 
- -52 
- -87 
- 1 -37 
-•12 
-1-85 
11 
(w) ... 
- -59 
- -91 
-1-38 
- -13 
- 1 -83 
Two things are at once obvious, (1) that the best result for every equation is 
given by the modern English female pelvis IV, (2) that the results for the two 
male pelves III and V are not very good. In the case of the equations (o), (v), 
(w), (?■), (s), (n) and (Jc), shown to have the least probable errors, the differences 
for the three female pelves, I, II, and IV, are all less than a centimetre except 
that of (k) for pelvis II, which is a little more. The best results for the English 
