Sexual Dimorphism
The sacrum is noticeably sexually dimorphic (differently-shaped in males and females).
In the female the sacrum is shorter and wider than in the male; the lower half forms a greater angle with the upper; the upper half is nearly straight, the lower half presenting the greatest amount of curvature. The bone is also directed more obliquely backward; this increases the size of the pelvic cavity and renders the sacrovertebral angle more prominent.
In the male the curvature is more evenly distributed over the whole length of the bone, and is altogether larger than in the female.
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