From these we may deduce 117° as the average sacro-vertebral angle in the male, and 130° as the same angle in the female. This remarkable average difference of 13° shows the much greater suddenness of the altera tion of direction in the spinal colutnn at its sacral extremity in the male subject, and is much greater than the difference of 5° to 6° in the pelvic. inclination of the sexes com pared in the tables of Weber and Naegele. But, in order more clearly to ascertain it the pelvic inclination invariably depended upon the variations of the sacro-vertebral angle, I compared the sacro-vertebral and pelvi-verte bral angles in nine male and nine female sub jects. In the former, I found the difference between these angles to vary from 5° to 35°, and, in the latter, to vary from 5° to 25°. In one instance only, in a male, the sucro-verte bral was as large as the pelvi-vertebral angle. From these observations, which were very carefully taken, it would seem that the total pelvic inclination does not exactly depend upon the sacro-vertebral angle ; and that, in males, where the average pelvic obliquity is a little greater, the average sacro-vertebral angle is much and disproportionately less. These results contradict, also, the assumption somewhat indefinitely stated by Blumenbach and others, on the authority of Bonaccioli, of Ferrara, that the sacrum inclines more backward, and that the sacro-vertebral angle is more promi nent in the female than in the male.
If the long diameter of the pubic symphysis be continued in its direction downwards and backwards, it will, in a well-formed female pelvis, cut the transverse vertical plane of the spine, also prolonged, at an angle of 50° to 55° Cfig.81. a b k),which will be found to be about the complementary or opposite angle to the sacro-vertebral angle in the female. This shows the general parallelism of the anterior or pubic wall of the pelvis, with the upper part of the posterior or sacral wall, although, on account of the rapid thinning of the latter as it descends, its pelvic surface seems to diverge from the pubis. Naegele found the
anterior pelvic wall to be often at right angles to the plane of the inlet, but the posterior generally somewhat more than a right angle. The great obliquity of the symphysis pubis to the transverse vertical plane of the vertebrx is one of the great characteristics of the human pelvis, as will be seen hereafter in the consider ation of the comparative anatomy of the pelvis. The angle formed by the symphysis pubis with the horizon is given by Cuvier from 75° to 95°. This is much too large ; from 35° to 40° is the true angle of the symphysis with the horizon in the human subject.
Ilio-isclzial angle.— While the pubis in the human subject is continued in the same right line with the mean direction of the ilium, which coincides with the cotylo-sacral rib of that bone, the ischium is inclined backwards, forming an angle of 110° to 115° with the same rib of bone (seefig...! 12.1. a c d, page 73.), so that, while the pubes are directed transversely with regard to the pelvic cavity, the ischia are directed vertically along, and forming the sides of the cavity. This arrangement will also be found to be an important characteristic of the human pelvis. when compared with those of the inferior mammalia, in which the reverse of this arrangement will be found to prevail, viz., the continuation of the ischia in the line of the ilia, and the formation of an ilio-pubic angle.
Angle of isclzio-pubic arch.— The angle at which the ischio-pubic rami tend toward each other, has been placed by Watt at 60° to 80' in the male, and 90° in the female; and by Scemmerring at 75° for the male, and_95° for the female (see figs. 83,80.).