INCLINATION OF THE PELVIS.-By making, in a well-formed subject, a direct vertical section of the spinal column, and drawing a line through the centres of the bodies of the axis and last lumbar vertebra, and by com paring with the transverse plane of such a pelvis to the vertebral column is obtained. The line so drawn will generally be found to line those of the superior and inferior outlets of the pelvis, the general inclination of the pass also through the bodies of the first dorsal and second lumbar vertebrm across their centres. The curved line of the vertebrm, in most well-formed subjects, cuts the straight line at these two points, in passing from the cervical to the dorsal, and from the latter to the lumbar curve.
The plane of the pelvic brim has been termed by Naegele and the brothers G. and E. Weber the superior pktne of the pelvis, and that of the inferior outlet the inferior plane. These observers measured the angle formed by these planes with the ground-level in the standing position, i. e. with the horizon, or with a plane drawn horizontally, at right angles, to the above-mentioned transverse vertical plane, which, in the erect posture, was found to be perpendicular to the base of support. The angle which the superior plane of the pelvis forms with the transverse vertical plane or with the horizon is termed by them the angle of inclination of the pelvis, or the pclvi vertebral angle (fig. 84. page 134.), (ae,e e).
lt is remarkable that, in man only, are the boundaries of the superior outlet in one plane, e. in wan only is the direction of the superior pubic ratnus in the sante plane with that of the eotylo-sacral rib of the ilium. In all other ani mals, as far as my own observations go, the pubis is bent backward or forward, so as to make an angle with the ilium, and the pelvi vertebral angle is thus resolved into two angles, a vertebro-iliac and an ilio-pubic.
The angle of the superior plane was found by the Webers on the dead body, by fixing the connected spinal column and pelvis of a recent well-made subject, in plaster of Paris, to preserve the natural position, then making through the whole ;a direct vertical section, and afterwards measuring off the angles.
On making a transverse vertical section through the centres of the heads of the femurs and cotyloid cavities, they also found that, when the body is in the erect position and the pelvis at the proper angle, the coty loid notch and depression, and the fibres of the ligamentum teres, have an almost directly vertical direction, and fall exactly in the trans verse vertical plane of the vertebrm (see fag. 87. page 140., in which the line a a' lies in the plane of the transverse vertical section). It will be further seen, by inspecting the figure, that this plane, being continued downwards, crosses the obturator foramina, and falls very nearly in the line of suture of the ischio-pubie rami. And this will be found to be the case, with a plumbline dropped from the sacral pro montory, which is cut by the above plane in the erect position of the pelvis. A detached pelvis may be placed in the erect living po sition, consequently, by keeping the poste rior part of the notch the most depending point of the cotyloid brim, and its inclinations will then accord with those taken in connec tion with the spine.
In the consideration of these pelvic angles it must be borne in mind that the direction of the curve of the three last lumbar vertebrx, below the point where the great dorsal con cavity terminates, is such that, if prolonged upwards, the axial line would pass out at the junction of the manubrium with the body of the sternum. This makes the pelvi-lumbar angle much kss in man than the whole pelvi vertebral ; a circumstance to be borne in mind in comparing them with those of animals. In fact, the transvertical section just mentioned passes through the body of the third lumbar vertebra considerably posterior to its centre in most cases (sce a, b, fig,. 84. page 131.).