By an inverse method, proceeding on Roederer's plan frorn the horizontal plane (Ag. 84. g,d), Naegele determined, with great care, the angle of the inferior plane of the pelvis in the living female. In 500 well-formed living females placed in the erect position, he mea sured the respective distances from the ground, of the tip of the coccyx, and of the lower border of the pubic symphysis. He found that in 454 the extremity of the coccyx was higher than the symphysis pubis, the greatest difference being 22 lines. In twenty-six only was it lower, the greatest difference here being 9 lines, and in twenty they were equal in height from the ground. In eleven pelves here he had the opportunity of verifying his observations after death, he found and figured one perfect pelvis, in which the tip of the coccyx was 8 lines higher than the lower border of the symphysis, which corresponded very nearly with the mean elevation of the coccyx above the symphysis, viz. 7-1 lines, drawn from the observations above detailed. From this he deduced the inferior angle of inclination of the pelvis (fg d) to be 10° to 11° with the horizon (g, d).
In a similar manner, in fifteen living niales the brothers Weber ascertained the range of the altitudes of the coccyx and pubis to be from 10 rnillitnetres, the extrente difference when the coccyx was lower, to 33.3 millinietres when the coccyx was higher than the lower border of the symphysis pubis, the mean height of the coccyx above the pubis being thus 23'1 millimetres. Then, by measuring the distance between the plumb lines dropped from each of these points, the coccyx and pubis, they ascertained the mean distance to be 75.8 millimetres. From these measurements they obtained the angle of the inferior pelvic plane with the horizon 16°-.51. By measuring, in two dead subjects, the depth of the symphysis pu bis, and the direct vertical distance from the tip of the coccyx to the sacral promontory, they deduced the angle of the superior pelvic plane. The superior angle, however, cannot with any certainty be calculated from the inferior in the living subject, on account of the un certain length and curve of the sacro-coccygeal column.
In a well-formed or standard pelvis the two lines of the superior and inferior planes, when prolonged anteriorly, cut each other about inch anterior to and below the pelvis (at c), containing an angle of about 50° (e c f); but this will vary with the leng,th of the sacro-coccygeal column.
According to Naegele the point at which the superior plane einerges posteriorly is also very variable. Most frequently it is the spinous process of the second lumbar vertebra, often that of the first, and sometimes between the second and third. Generally the upper
border of the symphysis pubis was 3 inches, 9 to 10 lines lower than the sacral promon tory, and on a level with the union of the second and third coccygeal bones. The sacro vertebral projection I have generally found to be about the level of the anterior superior iliac spine in the male, and a little below this point in the female, in a straight position of the body.
The following table shows the pelvic angles of inclination in the sexes, and their difference in this respect, and is drawn from the above mentioned experiments of the Webers on male, and of Naegele on female subjects.
By the inspection of the above table the greater inclination of the pelvis to the spine in the male will become evident, constituting another distinguishing characteristic of the sexes.
The older observers estimated the pelvic angles too low, as in the incorrect drawings of Albinus, Levret, and Cloquet, where the superior angle is given as 35° with the horizon, and, by Osiander, at 30°. Carus gives the superior at 55°, and the inferior at 11° with the horizon.
Angles of the anterior and posterior pelvic walls witl: the tranaverse vertical plane.— The pelvic inclination, in the opinion of Cru veilhier, depends upon the angle which the sacrum forms with the spinal column, giving more or less of obliquity to the innominate bones on each side. This angle (fig. 84. next page, a e and fig.112. 1. f a g, page 173), which may be called the saero-vertebral angle, I have, in as many opportunities as have oc curred to me, endeavoured to ascertain and establish, with a view of comparing it with the pelvi-vertebral angle in the two sexes. To do this I made a vertical section of the pelvis (with as many vertebr as possible attached to it), from behind forward in the median line, which showed clearly the angle made by the sacrum. Then, by intersecting the line of the transverse vertical plane of the spinal column drawn as before mentioned, by a line drawn in the mean direction of the three first sacral vertebra through the centre of their bodies, angles closely approximative to the sacro vertebral angle in the living subject were ob tained, showing the following results :— In twenty-five males, Nine were frotn 110° to 112°, five-from 115° to 117°, nine from 120° to 125°, and two only 130°.
In twenty-five females, Nine were from 120° to 125°, eight from 128° to 130°, five from 133° to 140°, two were 145°, and one, an aged subjea, 118° only.