THE MEASUREMENTS OF THE PELVIS, WITH SPECIAL REFERENCE TO OBSTETRIC PREDICTION
and length of the hip bone and the breadth of the sacrum have coefficients not very different from those of the transverse and inter-cristal diameters, and the height of the sacrum has a variability just about double that of any other bone measurement. The results are not surprising. Apart from the variation in a measurement due to individual differences, there are other causes for variation in the case of these measurements taken on old pelves. It is not always easy to obtain accurate
... n accurate measurements, especially of the diameters, and after death parts of the bone get worn away. The wearing away of the pubic crest, for example, and the difficulty which may be experienced in determining the lowest point of the symphysis, must be accountable to a great extent for the large variability of the pubic height. The height of the sacrum, being dependent on the number of vertebrae united to form that bone and on the integrity of the tip, which is apt to get worn, is more variable than the breadth of that bone and than the height and breadth of the hip bone. The extremities of these last are rounded and legs likely to be worn. The breadth is a little more variable than the height, and experience proves that, of the two, it is the more difficult to measure accurately. The diameters must depend on the same factors as the bones, the individual differences, wear and tear, and difficulty of getting accurate measurements. The last especially must be of importance here. The obstetric conjugate, for example, depends upon the position of the sacral promontory, and therefore on the number of vertebrae forming the sacrum and on the proper fitting together of the bones, on the integrity of the upper and posterior part of the pubic bone, and on the ease or difficulty with which its anterior extremity can be determined. How much of the variation is due to each of these factors it is impossible to say. In such a diameter as the transverse there is little likelihood that the parts of the bone forming its extremities will be much worn away, but it would be unwise to go beyond a general statement of this kind. The pubic height and the height of the sacrum vary more than any other measurement of a single bone with which we are acquainted. The measurements of the mandible come next in order. Their coefficients of variation, as given by C. D. Fawcett *, are, for the greatest height 9'93, for the greatest width at the condyles 7'46, and for the greatest width at the angles 7'62. The variations in the lengths of the long bones in different races (found for the French and Aino by Lee and Pearsont, for the Naqada by Warren+, and for other races by Pearson §) have been compared with those of our measurements. The coefficients have as their limits 4'17 and 7'00, most of them being less than 5'5; hence the measurements of the pelvic bones, other than the pubic height and the height of the sacrum already considered, although in some few cases varying to about the same extent as the lengths of the long bones, have, on the whole, a tendency to be more variable .