In mammalian anatomy, the cribriform plate (Latin for lit. sieve-shaped), horizontal lamina or lamina cribrosa is part of the ethmoid bone. It is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities. It supports the olfactory bulb, and is perforated by olfactory foramina for the passage of the olfactory nerves to the roof of the nasal cavity to convey smell to the brain. The foramina at the medial part of the groove allow the passage of the nerves to the upper part of the nasal septum while the foramina at the lateral part transmit the nerves to the superior nasal concha. A fractured cribriform plate can result in olfactory dysfunction, septal hematoma, cerebrospinal fluid rhinorrhoea (CSF rhinorrhoea), and possibly infection which can lead to meningitis. CSF rhinorrhoea (clear fluid leaking from the nose) is very serious and considered a medical emergency. Aging can cause the openings in the cribriform plate to close, pinching olfactory nerve fibers. A reduction in olfactory receptors, loss of blood flow, and thick nasal mucus can also cause an impaired sense of smell. Structure The cribriform plate is part of the ethmoid bone, which has a low density, and is spongy. It is narrow, with deep grooves supporting the olfactory bulb. Its anterior border, short and thick, articulates with the frontal bone. It has two small projecting alae (wings), which are received into corresponding depressions in the frontal bone to complete the foramen cecum. Its sides are smooth, and sometimes bulging due to the presence of a small air sinus in the interior. The crista galli projects upwards from the middle line of the cribriform plate. The long thin posterior border of the crista galli serves for the attachment of the falx cerebri. On either side of the crista galli, the cribriform plate is narrow and deeply grooved. At the front part of the cribriform plate, on either side of the crista galli, is a small fissure that is occupied by a process of dura mater. Lateral to this fissure is a notch or foramen which transmits the nasociliary nerve; from this notch a groove extends backward to the anterior ethmoidal foramen. Keros classification The Keros classification is a method of classifying the depth of the olfactory fossa. The depth of the olfactory fossa is determined by the height of the lateral lamella of the cribriform plate. Keros in 1962,