Ethmoidal labyrinth

The Labyrinth or Lateral Mass (labyrinthus ethmoidalis) consists of a number of thin-walled cellular cavities, the ethmoidal cells, arranged in three groups, anterior, middle, andposterior, and interposed between two vertical plates of bone; the lateral plate forms part of the orbit, the medial, part of the corresponding nasal cavity. In the disarticulated bone many of these cells are opened into, but when the bones are articulated, they are closed in at every part, except where they open into the nasal cavity.