Iliac Crest of the Os Coxae
The ilium is a Flat Bone and is part of the appendicular skeleton (limb support system).
Also known as: Hip Bone Ridge or Pelvic Wing Rim
Classification
The ilium is a Flat Bone and is part of the appendicular skeleton (limb support system).
Dimensions
Generally the widest part of the pelvic assembly, forming a long, thickened arched border that spans the top of the hip bone. In larger mammals, it provides a broad surface area proportional to the animal's weight-bearing needs.
Key Features
It is the thick, thickened upper border of the 'wing' of the hip. It has a rough texture that resembles the edge of a sturdy fan or a heavy s-shaped curve when viewed from above. It serves as the highest point of the pelvis and ends in distinctive blunt bumps at both the front and back.
Similar Bones
The shoulder blade (scapula) also has a long ridge and a flattened shape, but the hip ridge is much thicker and is part of a hollow, bowl-like structure, whereas the shoulder blade is relatively flat and lacks the large circular 'port hole' found nearby in the pelvis.
Across Species
In upright walkers, this ridge is short and curves dramatically forward to support internal organs. In four-legged animals like horses or dogs, the entire bone is elongated and positioned vertically to accommodate massive muscles used for running and leaping. In birds, this region is fused into a long, thin structure called a synsacrum to provide a rigid frame for flight.
Evolutionary History
This ridge has expanded significantly over millions of years. In early tetrapods, the hip was a small, simple rod. As land animals grew larger and began to lift their bodies off the ground, this bone flared out like a fan to provide more surface area for the powerful leg muscles required for mobility and stability away from the water.
Photography Tips
To capture this feature well, photograph the bone from a 'bird's eye view' looking down at the curve to show the S-shape, and also from the side to show the flare of the wing. Use a ruler or common object for scale, as size varies greatly between different species.
Notes
What is the blue highlighted part