Located below the frontal bone and in front of the sphenoid bone, this bone helps form the orbital and nasal cavities.

• A. Lacrimal bone
• B. Ethmoid bone
• C. Maxillary bone
• D. Zygomatic bone

Answer: (B)

The bone described is the ethmoid. It sits between the frontal bone above and in front of the sphenoid bone, and it helps form both the orbital cavities and the nasal cavity. Its orbital part contributes to the medial wall of each eye socket, while its nasal part includes the perpendicular plate forming the nasal septum and the ethmoidal labyrinth with air cells that line the upper portion of the nasal cavity and give rise to the middle nasal conchae. This dual role—part of the orbit and a central contributor to the nasal cavity—fits the description best. Other nearby bones contribute to either the orbit or the nasal cavity, but not both to the same extent.