Sphenoid and Ethmoid Bones
The ethmoid bone is an unpaired bone shaped like a cube that articulates with 13 cranial and facial bones. The cranial bones it articulates with, include the frontal and sphenoid bones. The ethmoid has three parts: the cribriform plate, the ethmoidal labyrinth, and perpendicular plate. The cribriform plate integrates into the ethmoidal notch of the frontal bone. Anteriorly, this articulation forms the foramen cecum. The crista galli is a midline upward projection to which the falx cerebri attaches. On either side of the crista galli, the cribriform plate has grooves that hold an olfactory bulb. Tiny foramina in the cribriform plate allow for the transmission of the olfactory nerves.
Extending inferiorly from the cribriform plate at the midline is the perpendicular plate. The perpendicular plate is almost entirely smooth except for a number of grooves on either side that lodge the olfactory nerves. Below the cribriform plate laterally lies the ethmoidal labyrinth which contains a network of thin-walled cavities, the ethmoidal cells.
The lateral surfaces of the labyrinth are covered by very thin, smooth plates called the lamina papyracea. The posterior parts of the medial surfaces of the labyrinth contain thin, curved bones that form the superior nasal conchae and have an associated superior meatus. Another curved projection forms the middle nasal conchae, which also have an associated meatus. Just inferior to the middle concha is a small, bony projection called the uncinate process, which forms a part of the medial wall of the maxillary sinus.