Without the corset, the pelvis remains fixed and furnishes the normal base of support for the thorax, which gains the erect position through the action of the muscles of the back acting on the vertebral column. Whereas, with the corset on, the pelvis is immobilized, and it follows the movements of the thorax. The movement of extension of the thorax, instead of taking place in the region between the false ribs and pelvis, takes place at the hip-joints—the vertebral column remains rigid, it takes no part in these movements. [Illustration: Fig. 18.—Muscles of the anterior surface of the trunk (O’Followell).] Then, as a result of the incurvation of the anterior surface of the trunk, there is an interference with the movements of extension of the spine and its immobilization, which causes the propulsion forward en masse of the abdominal contents. The anterior portion of the chest is shortened, and an exaggeration of the sacrolumbar angle is produced. On the sides of the body lateral flexion of the trunk is possible, through the contraction of the muscles between the chest and pelvis, but with corsets on this is impossible. The two cavities are fixed by the rigid armature which composes the corset. This not only prevents the lateral flexions of the body, but also causes an unnatural depression above the crests of the ilium. The waist is constricted to such an extent that the woman can only fasten her corsets in front by having them widely separated in the back. All these conditions cause a complete immobilization of the thorax on the pelvis, so that the movements of the upper part of the body are characteristic in corseted women, and she moves all in one piece. [Illustration: Fig. 19.—Diagram showing the action of the straight front corset (O’Followell). ] _The Straight Front Corset._—This corset, when worn loose, is a great improvement on the curved-front corset. When properly fitted, all the compression comes at the hips and across the lower part of the abdomen, which is lifted up, and the waist-line is increased in size. This corset has for its base of support the bony pelvis, and there should be sufficient space to easily introduce the hand between the lower part of the thorax and the corset. In this case there is great freedom of movement of the entire chest cavity, so that respiration is not nearly so much interfered with as in the curved-front corset, and if the corset is properly fitted, the lower part of the abdomen is raised together with the contained viscera, and, indeed, this style corset is prescribed in cases of prolapsus of the kidneys. By having the base of support from the bony pelvis, the chest is left free, and a good chest expansion and its throwing forward is favored, and at the same time an erect carriage is secured. The waist-line runs below the short ribs, which lengthens the waist, producing graceful lines without compression.