The difference in the form of the male and female pelvis is related to function. The male pelvis is adapted for support of a heavier physical build and muscles that are stronger. The female pelvis is adapted for childbearing rather than physical strength. Parts of the female pelvis outline the birth canal and must be wide enough for a baby to pass through during delivery.
The pelvis can be described as a large, shallow bowl. It sits at a forward angle between the abdominal cavity and the legs. Think of the hip bones as the upper rim of the bowl. The lower rim of the bowl is defined by the two pubic bones. The female pelvis is tilted far forward; it is wider and oval in shape. The male pelvis is tipped far less forward, is narrower and more heart-shaped. The bones of the male pelvis are thicker and heavier, while the bones of the female pelvis are lighter and thinner. Markings are more distinct on the male pelvis, whereas the female pelvis is smoother.
The pelvis is comprised of two hip bones, also called os coxae or coxal bones, the sacrum and the coccyx. The sacrum and coccyx are the last two distal portions of the spinal column. The hip bones are actually three separate bones that fuse completely during maturation. The three bones are the ilium, the ischium and the pubis. These bones come together and fuse at the acetabulum, the socket that receives the thigh bone, or femur. The female acetabulums are small in size and far apart compared to their male counterparts.
The left and right hip bones in the pelvis meet in back at the sacrum. The left and right pubic bones are joined by a fibrocartilage disc in front. This is called the pubic symphysis. If you draw a continuous line from the hip bones to the pubic symphysis, you can get a general idea of the shape and angle of the pelvic cavity. The pubic arch, found directly below the pubic symphysis, is a defining characteristic of the male and female pelvis. In the male, the pubic arch angle is very acute. The female pubic arch angle is more obtuse.
Sacrum and Coccyx
The curvature of the distal spine is also a defining characteristic. The coccyx in the male pelvis curves forward and is more rigid, while the female coccyx is straighter and more flexible. This helps women in childbirth. The sacrum is narrower and longer in the male than in the female.
The true pelvis is defined as the area circumscribed by the hip bones under the pelvic brim. The pelvic brim is a ridge running from the base of the sacrum around the inside of the hip bone and to the pubic crest. The cavity circumscribed by the true pelvis is important in childbirth. The true pelvis determines whether normal, uncomplicated, vaginal delivery is possible. If the dimensions of the true pelvis are not sufficient or if the angle of the coccyx is too sharp, the birth canal is compromised and the baby may not pass easily through it.