The ethmoid bone is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a spongy construction. The ethmoid bone is one of the bones that make up the orbit of the eye.
The orbital or horizontal part of the frontal bone consists of two thin triangular plates, the orbital plates, which form the vaults of the orbits, and are separated from one another by a median gap, the ethmoidal notch.
In the ethmoid bone, a sickle shaped projection, the uncinate process, projects posteroinferiorly from the ethmoid labyrinth. Between the posterior edge of this process and the anterior surface of the ethmoid bulla, there is a two-dimensional space, resembling a crescent shape. This space continues laterally as a three-dimensional slit-like space - the ethmoidal infundibulum. This is bounded by the uncinate process, medially, the orbital lamina of ethmoid bone, laterally, and the ethmoidal bulla, posterosuperiorly. This concept is easier to understand if one imagine the infundibulum as a prism so that its medial face is the hiatus semilunaris. The "lateral face" of this infundibulum contains the ostium of the maxillary sinus, which, therefore, opens into the infundibulum.
The ethmoid sinus or ethmoidal air cells of the ethmoid bone is one of the four paired paranasal sinuses. The cells are variable in both size and number in the lateral mass of each of the ethmoid bones and cannot be palpated during an extraoral examination. They are divided into anterior and posterior groups. The ethmoidal air cells are numerous thin-walled cavities situated in the ethmoidal labyrinth and completed by the frontal, maxilla, lacrimal, sphenoidal, and palatine bones. They lie between the upper parts of the nasal cavities and the orbits, and are separated from these cavities by thin bony lamellae.
The ophthalmic nerve is the first branch of the trigeminal nerve. The ophthalmic nerve is a sensory nerve mostly carrying general somatic afferent fibers that transmit sensory information to the CNS from structures of the eyeball, the skin of the upper face and anterior scalp, the lining of the upper part of the nasal cavity and air cells, and the meninges of the anterior cranial fossa. Some of ophthalmic nerve branches also convey parasympathetic fibers.
The semilunar hiatus or hiatus semilunaris, is a crescent-shaped groove in the lateral wall of the nasal cavity just inferior to the ethmoid bulla. It is the location of the openings for the frontal sinus, maxillary sinus, and anterior ethmoidal sinus. It is bounded inferiorly and anteriorly by the sharp concave margin of the uncinate process of the ethmoid bone, superiorly by the ethmoid bulla, and posteriorly by the middle nasal concha.
The Labyrinth or Lateral Mass of the ethmoid bone 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 plate forms part of the 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.
The anterior ethmoidal artery, also anterior ethmoid artery is an artery of the head.
The anterior ethmoidal foramen is a small opening in the ethmoid bone in the skull.
The anterior ethmoidal nerve is a nerve which provides sensory branches to the nasal cavity. The nerve is the continuation of the nasociliary nerve after it enters the anterior ethmoidal foramen into the anterior ethmoidal air cells. The nasociliary nerve arises from the Ophthalmic division of the Trigeminal nerve within the orbit. The anterior ethmoidal nerve arises only after the nasociliary has given off its four branches - 1) Ramus communicans to ciliary ganglion, 2) Long ciliary nerves, 3) infratrochlear nerve, 4) Posterior ethmoidal nerve.
On the lateral wall of the middle meatus is a curved fissure, the hiatus semilunaris, limited below by the edge of the uncinate process of the ethmoid and above by an elevation named the ethmoid bulla ; the anterior ethmoidal cells are contained within this bulla and open on or near to it.
The anterior cranial fossa is a depression in the floor of the cranial base which houses the projecting frontal lobes of the brain. It is formed by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the small wings and front part of the body of the sphenoid; it is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the chiasmatic groove. The lesser wings of the sphenoid separate the anterior and middle fossae.
The orbital process of the palatine bone is placed on a higher level than the sphenoidal, and is directed upward and lateralward from the front of the vertical part, to which it is connected by a constricted neck. It presents five surfaces, which enclose an air cell. Of these surfaces, three are articular and two non-articular.
The superior surface of the body of the sphenoid bone presents in front a prominent spine, the ethmoidal spine, for articulation with the cribriform plate of the ethmoid; behind this is a smooth surface slightly raised in the middle line, and grooved on either side for the olfactory lobes of the brain.
The frontal process of maxilla is a strong plate, which projects upward, medialward, and backward from the maxilla, forming part of the lateral boundary of the nose.
The body of the sphenoid bone, more or less cubical in shape, is hollowed out in its interior to form two large cavities, the sphenoidal sinuses, which are separated from each other by a septum.
Behind the lacrimal process of the inferior nasal conchae lies a broad, thin plate, the ethmoidal process, which ascends to join the uncinate process of the ethmoid; from its lower border a thin lamina, the maxillary process, curves downward and lateralward; it articulates with the maxilla and forms a part of the medial wall of the maxillary sinus.
A nasal meatus is a nasal passage of the nasal cavity, of which there are three; the superior meatus, middle meatus and inferior meatus. These nasal meatuses are also known as meatus nasi superior, meatus nasi medius, and meatus nasi inferior..
A plate in animal anatomy may refer to several things:
