Which bone joins all of the bones of the cranium together?

• A. Sphenoid bone
• B. Temporal bone
• C. Ethmoid bone
• D. Occipital bone

Answer: (A)

The sphenoid bone acts as the keystone of the skull, sitting in the middle of the cranial base and forming joints with nearly every other cranial bone. Its central position and multiple articulations allow it to connect the frontal, parietal, temporal, occipital, and ethmoid bones (along with other facial bones in parts of the skull). This widespread set of connections is what holds the cranial bones together, giving structure and stability to the cranium. The other bones listed do not connect all the cranial bones on their own: the temporal, ethmoid, and occipital bones each articulate with several nearby bones, but not with every cranial bone, so they can’t fulfill the role the sphenoid does.