. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 196 PELVIS. necessary that the line of gravity of the whole body—viz. that from the lower centre—should Fig. A. Diagram of the lines and centres of gravity of the trunk, a b; and of the whole body, c d. B. Outline of the lines of pressure in the pelvis and legs in the ovate rickety distortion, during the standing posture.—a b lines of direction of .the pressure of the heads of the femurs in the ace- tabula,—upwards and outwards. c. Outline of the pelvis and legs in the angular rostrated pelvis ot the adult, resulti
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 196 PELVIS. necessary that the line of gravity of the whole body—viz. that from the lower centre—should Fig. A. Diagram of the lines and centres of gravity of the trunk, a b; and of the whole body, c d. B. Outline of the lines of pressure in the pelvis and legs in the ovate rickety distortion, during the standing posture.—a b lines of direction of .the pressure of the heads of the femurs in the ace- tabula,—upwards and outwards. c. Outline of the pelvis and legs in the angular rostrated pelvis ot the adult, resulting from molli- ttes ossium. a b, a c, direction of pressure in the acetabula when the legs are not deformed,— upwards and inwards. D. A similar outline in the angular rickety pelvis of the child, when the legs are bent outwards, — di- rection of pressure inwards. E. Outline of abnormal antero-posterior curves of the spine, pelvis, and legs, a b, direction of the pressure in the acetabuia backwards increased by the forward curve of the femora, c d, line of traction of the 'psoas muscles increasing the de- formity of the pelvis. fall anywhere between the extent of longitude of the feet {c d). If the trunk, however, bend forward, its centre and line of gravity is advanced beyond that of the whole body, and a share of the sup- port of the trunk, equivalent to the degree of distance of two lines (b,d),falls upon the muscles and ligaments of the posterior part of thespine,and a cor responding strain upon their attachments to the sacrum and posterior part of the pelvis. This instance may be taken as an example of many others, in which the me- chanical position of the line of gravity in- fluences muscular action, the effects of both falling upon the lines of pressure and support in the pelvis. For the preservation of the sitting position, it is only necessary that the line of gravity of the trunk (« b) should fall within the extent of the basis of support, which is
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