. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. PELVIS. 139 8'7 millimetres above the sacro-lumbar joint, or just above the pelvic arch. All weight on the arch, such as that of the trunk, is sup- ported most easily when its line of gravity falls through this part, and coincides with that of the whole body in the transverse vertical plane, and the trunk will be found to be thrown into such a position, when supporting heavy weights, as will tend to produce this effect. And, according to the researches of Rokitanski, when the sacro-vertebral angle and pelvic inclination
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. PELVIS. 139 8'7 millimetres above the sacro-lumbar joint, or just above the pelvic arch. All weight on the arch, such as that of the trunk, is sup- ported most easily when its line of gravity falls through this part, and coincides with that of the whole body in the transverse vertical plane, and the trunk will be found to be thrown into such a position, when supporting heavy weights, as will tend to produce this effect. And, according to the researches of Rokitanski, when the sacro-vertebral angle and pelvic inclination is increased, as by hip disease, there is always a compensatory curve of the spine backward, to keep the centre of gravity above this point. In artificial constructions for the purpose of transmitting a weight downwards from a central to two lateral points, a segment of a circle, or arch is most commonly made use of, and generally consists of two lateral curved portions, composed of separate parts or voussoirs, with an interposed substance between them called a keystone or crown- piece, of a wedge shape, and placed with the broad end uppermost. This wedge shape exactly corresponds to the interval which would be left between the lateral curved pieces, having their ends cut square. Any force operating on the keystone from above tends only to drive the broader part of the wedge further between the lateral pieces, at the same time pressing them nearer to each other, and so to increase the firmness of the arch, so long as the extremities are firmly fixed in the ground and prevented from start- ing outwards, which is generally accomplished by means of abutments. Constructed upon this plan, the pelvis pre- sents two lateral curved thickened buttresses or columns, passing from the cotyloid to the sacro-iliac articulations, and two others pass- ing on a plane posterior to these from the tuberosities of the ischia along their de- scending rami, and through the ilia to the same sacro-ili
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