Which of the following bones is not paired?

The vomer is a single bone that forms part of the nasal septum, which separates the two nasal cavities. It is classified as an unpaired bone because it exists as a singular structure in the skull, unlike paired bones that come in left and right counterparts.

The ethmoid bone, while playing a crucial role in the structure of the skull and nasal cavity, is also an unpaired bone, as it is a single bone located at the roof of the nasal cavity and between the orbits. The maxilla and palatine bones, on the other hand, are paired bones as they each exist as a set: one on the left and one on the right side of the face.

Therefore, the vomer is the correct answer, as it is the only bone listed that is not paired.