Location of Foramina Cribrosa
The openings are located in the cribriform plate (Lamina cribrosa), which is the horizontal part of the unpaired, air-containing ethmoid bone (Os ethmoidale).
The ethmoid bone consists of four parts:
- Cribriform plate (Lamina cribrosa) — contains the foramina cribrosa, the crista galli (Crista galli), and its ala (Ala crista galli).
- Perpendicular plate (Lamina perpendicularis) — the vertical part that contributes to the formation of the bony nasal septum.
- Ethmoidal labyrinths (Labyrinthus ethmoidalis) — paired structures containing ethmoidal air cells (Cellulae ethmoidales) and the superior and middle nasal conchae.
Topography and Contribution to Skull Walls
The cribriform plate with its foramina is a key element of two major cranial regions:
- Roof of the bony nasal cavity (Cavitas nasalis ossea). This roof is formed by the cribriform plate of the ethmoid bone along with the nasal bones, the nasal part of the frontal bone, and the body of the sphenoid bone. The nasal cavity is trapezoidal; its anterior boundary is the piriform aperture (Apertura piriformis), bounded by the nasal bone, nasal notch, and the anterior nasal spine of the maxilla. The posterior boundaries are the choanae (Choanae). In the midline, the cavity is divided by the bony nasal septum (Septum nasi osseum), formed by the perpendicular plate of the ethmoid bone, the vomer (Vomer), the nasal spine of the frontal bone, and the sphenoidal crest.
- Anterior cranial fossa (Fossa cranii anterior). This fossa is bounded anteriorly by the frontal squama and posteriorly by the lesser wings of the sphenoid bone and the prechiasmatic sulcus. Through the foramina cribrosa, the anterior cranial fossa communicates with the nasal cavity. In addition to the foramina cribrosa, the anterior cranial fossa communicates with the nasal cavity via the foramen caecum (Foramen caecum), which transmits an emissary vein.
Contents of Foramina Cribrosa
The openings serve as passages for the following structures:
- Olfactory nerve fibers (Fila olfactoria).
- Meningeal branches.
Distinction: Anterior and Posterior Ethmoidal Foramina
Cranial anatomy also defines the anterior and posterior ethmoidal foramina (Foramina ethmoidalia anterior et posterior). Unlike the foramina cribrosa, these are located on the medial wall of the orbit, transmit the neurovascular bundles of the same name, and connect the orbit to the ethmoidal air cells, the nasal cavity, and the anterior cranial fossa. The medial wall of the orbit is formed by the frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid bone, and the lateral surface of the body of the sphenoid bone. The orbit is shaped like a pyramid, with its apex corresponding to the optic canal (Canalis opticus).