Which of the following is not a part of ethmoid bone?
Correct Answer: Inferior turbinate
Description: ANSWER: (B) Inferior turbinateREF: Gray's anatomy 40th ed chapter 29, Rhinology and Facial Plastic Surgery By Fred J. Stucker, Chris de Souza, Guy S. Kenyon, Timothy S. Lian, Wolfgang Draf, Bernhard Schick page 502Note: inferior turbinate is a separate bone in itself.ETHMOID BONE:The ethmoid bone is cuboidal and fragile, and lies anteriorly in the cranial base. It contributes to the medial orbital walls, nasal septum, and the roof and lateral walls of the nasal cavity. It has a horizontal, perforated cribriform plate, a median perpendicular plate, and two lateral labyrinths which contain the ethmoidal air cells.The cribriform plate:The cribriform plate fills the ethmoidal notch of the frontal bone and forms a large part of the nasal roof. It derives its name from the fact that it is penetrated by numerous foramina that transmit branches of the olfactory nerves and their associated meninges.Ethmoid Hone viewed from behind.A thick, smooth, triangular, median crista galli projects up from the horizontally aligned plate of bone. The falx cerebri is attached to its thin and curved posterior border. Its shorter, thick, anterior border joins the frontal bone by two small alae, to complete the foramen caecum.On both sides of the crista galli, the cribriform plate is narrow and depressed: it is related to the gyrus rectus and the olfactory bulb which lie above it. On each side of the crista anteriorly there is a small slit occupied by dura mater, and just anterolateral to the slit, a foramen which transmits the anterior ethmoidal nerve and vessels to the nasal cavityThe perpendicular plate : It is thin, flat, quadrilateral and median, and it descends from the cribriform plate to form the upper part of the nasal septum. Its anterior border meets the nasal spine of the frontal bone and the crests of the nasal bones. Its posterior border joins the crest of the body of the sphenoid bone above and vomer below.The ethmoidal labyrinths:It consist of thin-ivalled ethmoidal air cells between two vertical plates and are arranged in anterior, middle and posterior groups. On average there are 11 anterior ethmoidal air cells, 3 middle, and 6 posterior.The posterior group (sometimes the posterior ethmoidal sinus) drains into the superior meatus above the middle nasal concha; sometimes one or more opens into the sphenoidal sinus.The middle group (sometimes the middle ethmoidal sinus) drains into the middle meatus of the nose on or above the bulla ethmoidalisThe anterior group (sometimes the anterior ethmoidal sinus) drains into the middle meatus of the nose by way of the infundibulum. Agger nasi air cells, are the most anterior ethmoidal air cells, lying anterolateral and inferior to the frontoethmoidal recess and anterior and above the attachment of the middle turbinate. They are located within the lacrimal bone and therefore have as lateral relations the orbit, the lacrimal sac and the nasolacrimal duct.A thin, curved uncinate process, variable in size, projects posteroinferiorly from the labyrinth. The upper edge of this process is a medial boundary of the hiatus semilunarisin the middle meatusThe medial surface of the labyrinth forms part of the lateral nasal wall as a thin lamella descending from the inferior surface of the cribriform plate to end as the convoluted middle nasal conchaPosteriorly it is divided by the narrow, oblique superior meatus, bounded above by the thin, curved superior nasal concha. Posterior ethmoidal air cells open into this meatusMiddle ethmoidal air cells produce a swelling (bulla ethmoidalis) on the lateral wall of the middle meatus. These air cells open into the meatus, on the bulla or above it. A curved infundibulum extends up and forwards from the middle meatus and communicates with the anterior ethmoidal sinuses. In more than 50% of crania it continues up as the frontonasal duct to include the drainage point for the frontal sinus.
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