THE PREPUBERAL PUBIC SYMPHYSIS AND UTERUS IN THE MOUSE: THEIR RESPONSE TO ESTROGEN AND RELAXIN1

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Abstract
THERE is a marked sexual dimorphism of the pelvis in adult mice. The pelvis of the female mouse differs from that of the male by having smaller bones, a greater ischio-pubic angle and a more posteriorly placed pubic symphysis (Gardner, 1936). These differences develop even when mice are gonadectomized at 3 weeks of age (Crelin and Haines, 1955). Puberty in the mouse usually occurs shortly after the 6th postnatal week (Allen, 1923). Following puberty the medial ends of the female’s pubic bones resorb partially at the symphysis. This does not occur in mice ovariectomized before puberty (Crelin and Haines, 1955). Pubic bone resorption occurs in both gonadectomized and intact estrogen-treated mice. (Gardner, 1936; Hall, 1950; Crelin, 1954a). During the estrous cycle in mice a slight interpubic separation occurs (Kliman et al., 1952). During the first pregnancy the interpubic separation is increased greatly and the medial ends of the pubic bones undergo further resorption.