Sphenoid
Irregular bone; part of the axial skeleton (core framework)
Also known as: Butterfly Bone, Wasp Bone, Keystone Bone
Classification
Irregular bone; part of the axial skeleton (core framework)
Dimensions
This bone spans the entire width of the central skull base. It is wider than it is long, typically matching the internal span from temple to temple.
Key Features
The sphenoid is instantly recognizable for its resemblance to a butterfly or a moth with outstretched wings. It features a central body with two sets of 'wings' (one larger pair and one smaller pair) and two leg-like structures hanging from the bottom. The center contains a distinct scoop-like cradle that resembles a Turkish saddle.
Similar Bones
The ethmoid bone, which sits just in front of it, can be confused with the sphenoid's central body, but the ethmoid is much smaller, more porous, and lacks the dramatic spreading wings. Fragmented pieces of the temporal bone might look similar, but they are denser and contain the ear canal structures.
Across Species
In humans, the sphenoid is a single fused unit that anchors all other skull bones. In many other mammals, it remains as separate pieces. In birds, the sphenoid is highly specialized to help lighten the skull for flight while providing strong attachment points for large jaw muscles and supporting the large optic nerves required for keen eyesight.
Evolutionary History
The sphenoid has deep roots reaching back to early jawed vertebrates. Originally composed of several smaller distinct plates, these elements merged over millions of years to provide a stable platform for the developing brain. Its shape has shifted significantly as primates evolved flatter faces and larger brain cavities, moving from a long, narrow base to its modern, expansive butterfly-like form.
Photography Tips
To capture the sphenoid's unique shape, it is best photographed from above to show the wing-like spread or from the front to see the 'butterfly' face. Place it on a dark, non-reflective background with a soft light source from the side to highlight the delicate ridges and the central cradle.
Notes
What is the highlighted blue part