Os, (from Ethmoides 3700 a sieve, and a form). Cribriforme, cribrosum, and coliforme os; fora-minulentum; spongiosum os. This bone is placed between the two orbits of the eyes, where a notch is left for its insertion. The cribriform lamella is the internal plain, thin, horizontal plate, which hath a middle eminence called crista galli, to which the beginning of the falciform process is attached: round the crista galli, except at the hind part, this lamella is pierced obliquely by many small foramina, through which the filaments of the olfactory nerves pass. From the middle of the cribriform lamella, the nasal lamella rises extremely thin, but at its anterior extremity it becomes thicker. At a little distance from each side of this lamella, a cellular bony substance is observable: the figure of the cells is uncertain; they communicate with the frontal sinuses, and with the cavity of the nose, and are the external lateral portion of the ethmoid bone: their outward posterior surface is smooth, called os planum; and it makes a part of the orbit. The ossa spongiosa, or turbinata superiora, are situated at the inferior parts of the cellules; their figure is oblong, and they are sharp at their extremities.

The cribriform lamella is the body, as it were, of the ethmoid bone; and it is so thin, that it may easily be penetrated by a probe: when hurt, the accident is usually fatal.