Henry Gray (18251861). Anatomy of the Human Body. 1918.
The Lower Circumference.The lower circumference of the pelvis is very irregular; the space enclosed by it is named the inferior aperture or outlet (apertura pelvis [minoris] inferior) (Fig. 239), and is bounded behind by the point of the coccyx, and laterally by the ischial tuberosities. These eminences are separated by three notches: one in front, the pubic arch, formed by the convergence of the inferior rami of the ischium and pubis on either side. The other notches, one on either side, are formed by the sacrum and coccyx behind, the ischium in front, and the ilium above; they are called the sciatic notches; in the natural state they are converted into foramina by the sacrotuberous and sacrospinous ligaments. When the ligaments are in situ, the inferior aperture of the pelvis is lozenge-shaped, bounded, in front, by the pubic arcuate ligament and the inferior rami of the pubes and ischia; laterally, by the ischial tuberosities; and behind, by the sacrotuberous ligaments and the tip of the coccyx.
The diameters of the outlet of the pelvis are two, antero-posterior and transverse. The antero-posterior diameter extends from the tip of the coccyx to the lower part of the pubic symphysis; its measurement is from 90 to 115 mm. in the female. It varies with the length of the coccyx, and is capable of increase or diminution, on account of the mobility of that bone. The transverse diameter, measured between the posterior parts of the ischial tuberosities, is about 115 mm. in the female.1
Axes (Fig. 240).A line at right angles to the plane of the superior aperture at its center would, if prolonged, pass through the umbilicus above and the middle of the coccyx below; the axis of the superior aperture is therefore directed downward and backward. The axis of the inferior aperture, produced upward, would touch the base of the sacrum, and is also directed downward, and slightly backward. The axis of the cavityi. e., an axis at right angles to a series of planes between those of the superior and inferior apertures
Note 1. The measurements of the pelvis given above are fairly accurate, but different figures are given by various authors no doubt due mainly to differences in the physique and stature of the population from whom the measurements have been taken. [back]