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Station 2: The Pelvis
Station 2: The Pelvis
The pelvis is a bony structure formed by two hipbones (os coxae) and a triangular bone called the sacrum. The os coxae can be further broken down into the ischium, ilium, and pubis.
The pelves of bipeds differ from the pelves of quadrupeds because of how bipeds and quadrupeds distribute their weight to stabilize and balance during locomotion. When you walk, you stand on one leg while you swing the other leg to move. As a biped, you must keep your center of gravity over the standing leg and not fall to the unsupported side.
In contrast, quadrupeds walk by by moving their left hind leg first then their left foreleg. This motion ensures that the quaduped’s body is supported at all times by three feet on the ground which form a triangle of stability.
In quadrupeds, the pelvis does not need to support the weight of the body, so it is more gracile (thin). The pelvis is long and narrow. The iliac blades (the two sides of the ilium) are tall and flat and situated on the back of the animal. The sacrum is long and narrow. Because the iliac blades are long, the distance from the hip joint (acetabulum) to the sacrum is relatively large.
In bipeds, the pelvis bears the weight of the entire body, so it is more robust (thick). The pelvis is short and wide. The iliac blades are wide, and short and curved, creating a bowl-shape. The sacrum is short and wide. The shortening and broadening of the ilium also places the acetabulum closer to the sacrum. These boney adaptations reflect the increased and repositioned musculature of the hips that assist in propulsion and stability during bipedal locomotion.
Comparative anatomy
Comparative anatomy
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