Which of the following is not a facial bone?

The sphenoid bone is correctly identified as not being a facial bone because it is primarily a cranial bone that contributes to the base of the skull. While it plays a crucial role in the structure of the skull and forms part of the orbit (eye socket), it does not comprise the facial skeleton that supports the structures of the face.

In contrast, the mandible, maxilla, and zygomatic bones are all classified as facial bones. The mandible is the lower jawbone, the maxilla forms the upper jaw and parts of the orbits and nasal cavity, and the zygomatic bones are commonly known as the cheekbones. Each of these bones is integral to the structure and function of the face, providing support and attachment points for facial muscles, as well as forming the cavities that house the eyes and mouth.