Hueso Etmoides

The ethmoid bone is exceedingly light and spongy, and cubical in shape; it is situated at the anterior part of the base of the cranium, between the two orbits, at the roof of the nose, and contributes to each of these cavities. It consists of four parts: a horizontal or cribriform plate, forming part of the base of the cranium; a perpendicular plate, constituting part of the nasal septum; and twolateral masses or labyrinths. Hueso impar, medio y simétrico, situado por delante del esfenoides, en la escotadura etmoidal del frontal, se encuentra en la base del cráneo, por lo que contribuye a la formación de su piso y al mismo tiempo forma otras estructuras de la cara. Hemos de distinguir en él tres partes: 
LAMINA VERTICAL
Cortada transversalmente por la lámina horizontal que la divide endos partes; una por encima: la apófisis cristagalli y otra que está por debajo: la lámina perpendicular del etmoides.
LAMINA HORIZONTAL
* de forma cuadrilátera, se articula con la incisura etmoidal del frontal en los bordes laterales. La presencia del proceso crista galli divide esta superficie en dos surcos: los canales olfatorios, perforados por orificios; se le llama lamina cribosa, enella se encuentran los bulbos olfatorios.

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 withthe 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 fromthe medial foramina on the cribriform plate and lodge filaments of the olfactory nerves. |    3 |
  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. |    4 |
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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, bythe 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 by articulation with the sphenoidal concha and orbital process of thepalatine. The lateral surface (Fig. 152) is formed of a thin, smooth, oblong plate, the lamina papyracea (os planum), which covers in the middle and posterior ethmoidal cells and forms a large part of the medial wall of the orbit; it articulates above with the orbital plate of the frontal bone, below with the maxilla and orbital process of the palatine, in front with the lacrimal, and behind withthe sphenoid. |    5 |
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  The medial surface of the labyrinth (Fig. 153) forms part of the lateral wall of the corresponding nasal cavity. It consists of a thin lamella, which descends from the under surface of the cribriform plate, and ends below in a free, convoluted margin, themiddle nasal concha. It is rough, and marked above by numerous grooves, directed nearly vertically downward...