Anatomical Planes

impact the ability of the female in particular to have a successful childbirth. Let’s review these:

• Pelvic size—the male pelvis tends to be smaller than the female pelvis, even though the bones are thicker. The female has lighter bones but a bigger pelvis overall, which gives a woman wider hips. • Sacrum—the sacrum forms the broad base of the vertebral column and is a posterior structure the fetus must pass near during childbirth. In males, the sacrum is more curved, longer, and narrower. In females, the sacrum is shorter, wider, and less curved. Too great a curvature in females would impact the ability of the fetus to pass through the pelvis in the birth process. • Pelvic inlet and outlet—the pelvic inlet is the first bony barrier to effective passage of the fetus in childbirth. In females, the pelvic inlet is roughly oval in shape, while in males, this structure is heart-shaped. The pelvic outlet is below the inlet and is narrower in males than it is in females. Again, the goal is to have a birth passage that is more efficient in females than it is in males. • Coccyx—this is the small triangular lower tip of the vertebral column. In males, the coccyx is immobile and is projected inward. In females, the coccyx is straighter and is considerably more flexible than in males.

Again, each of these pelvic bone structures represents an evolutionary difference between men and women that together account for the ability of the female sex to give birth much more efficiently than the male sex. Women who, for whatever reason, were born with a more android-shaped pelvis will not necessarily have more difficulty getting pregnant but will have a harder time achieving a vaginal birth.

ANATOMICAL PLANES

Let’s start our discussion of reproductive anatomy by reviewing standard anatomical planes. The body can be divided up into three distinct planes – the sagittal plane, the coronal plane, and the transverse plane. Figure 2 shows what these common anatomical planes look like:

Figure 2.

The three anatomical planes are perpendicular to each other and are based on the standard anatomical position. The standard anatomical position assumes an individual is standing, facing forward, with the palms of his or her hands facing forward as well.

• In standard anatomical position, the sagittal plane divides the body in half creating a left side and a right side. The sagittal plane runs vertically from head to toe. • The parasagittal plane is any vertical plane that is on either side of the central sagittal plane. It does not divide the body into two equal halves. • Like the sagittal plane, the coronal plane also runs from head to toe. However, the coronal plane divides the body into front and back. • The transverse plane, which is also called the horizontal plane, divides the body into superior and inferior sections – or top and bottom sections. The transverse plane runs parallel to the ground in a person in standard anatomical position.