Sphenoid
Irregular bone, axial skeleton
Also known as: Butterfly Bone, Wasp Bone
Classification
Irregular bone, axial skeleton
Dimensions
Typically moderately sized and broadly spanning the width of the skull, this bone is notable for its expansive horizontal 'wings' and central body, making it wider than it is long.
Key Features
The most distinctive feature is its resemblance to a butterfly or moth with wings outstretched. It contains several small circular openings for nerves to pass through and a central cradle on its top surface that resembles a tiny saddle.
Similar Bones
From the outside of a full skull, parts of it can be mistaken for the temple (temporal bone) or the cheekbone (zygomatic bone), but the sphenoid is the only one that stretches all the way across the internal floor of the skull from one side to the other.
Across Species
While in humans this bone provides a wide base for a large brain, in other mammals like horses or dogs, it is more elongated to accommodate a longer snout. In birds, the equivalent structure is highly fused to create a lightweight, rigid platform for the large eyes required for flight.
Evolutionary History
Decended from several separate elements in early tetrapods, these pieces fused together over millions of years to form a single, complex anchor at the base of the skull. This fusion provided the structural integrity necessary as vertebrate brains became larger and more complex.
Photography Tips
To capture the full 'butterfly' shape, photograph the bone from directly above or below. Using a high-contrast background helps show the delicate edges of the wings and the various small openings in the center.
Notes
What is the blue highlighted part?