|Henry Gray (1825–1861). Anatomy of the Human Body. 1918.|
|plate, on either side of the crista galli, is a small fissure which 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.|
FIG. 150– Perpendicular plate of ethmoid. Shown by removing the right labyrinth. (See enlarged image)
Perpendicular Plate (lamina perpendicularis; vertical plate).—The perpendicular plate (Figs. 150, 151) is a thin, flattened lamina, polygonal in form, which descends from the under surface of the cribriform plate, and assists in forming the septum of the nose; it is generally deflected a little to one or other side. The anterior border articulates with the spine of the frontal bone and the crest of the nasal bones. The posterior border articulates by its upper half with the sphenoidal crest, by its lower with the vomer. The inferior border is thicker than the posterior, and serves for the attachment of the septal cartilage of the nose. The surfaces of the plate are smooth, except above, where numerous grooves and canals are seen; these lead from the medial foramina on the cribriform plate and lodge filaments of the olfactory nerves.
FIG. 151– Ethmoid bone from behind. (See enlarged image)
| 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, and posterior, 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.|
Surfaces.—The upper surface of the labyrinth (Fig. 149) presents a number of half-broken cells, the walls of which are completed, in the articulated skull, by the edges of the ethmoidal notch of the frontal bone. Crossing this surface are two grooves, converted into canals by articulation with the frontal; they are the anterior and posterior ethmoidal canals, and open on the inner wall of the orbit. The posterior surface presents large irregular cellular cavities, which are closed in