Occipital Bone
Flat bone and irregular bone, part of the core axial skeleton
Also known as: Base of the skull, back of the head
Classification
Flat bone and irregular bone, part of the core axial skeleton
Dimensions
Forms the lower back portion of the cranium, featuring a bowl-like curve with a distinctive large opening at the bottom and smooth outward-curving outer surfaces.
Key Features
The most defining feature is the large central oval opening through which the brainstem connects to the body. Flanking this opening are two smooth, rounded bumps that serve as rocker surfaces, plus a prominent ridge running across the outer back surface.
Similar Bones
Can be confused with other flat cranial bones or portions of vertebrae. However, the presence of the massive central hole and the smooth rocking bumps make this specific skull base entirely unique and easy to separate from standard flat skull plates.
Across Species
In many four-legged animals, the connection points for the neck sit further back on the skull to help balance the head forward, whereas in upright walkers, these connection points sit directly underneath the head to balance its weight evenly atop the spine. Birds have a single smooth knob for neck attachment, while mammals feature a pair of distinct bumps on either side of the opening.
Evolutionary History
This bone originates from ancient gill arch supports and protective head plates found in early fish. Over millions of years of vertebrate evolution, these various protective plates fused together to form a solid, unified skull base that encloses and protects the brain while leaving a clear gateway for the spinal cord.
Photography Tips
Photograph from a direct underside view to clearly capture the large central opening and the paired rocking bumps. Use soft, directional lighting to highlight the ridges and contours across the surface, and include a coin or small ruler nearby for scale.