mesethmoid


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Related to mesethmoid: mesethmoid bone

mesethmoid

[me′zeth‚mȯid]
(anatomy)
A bone or cartilage in the center of the ethmoid region of the vertebrate skull; usually constitutes the greater portion of the nasal septum.
References in periodicals archive ?
2), and is supported by a single synapomorphy: anteroventral margin of prevomer situates well posteriorly to anteroventral margin of mesethmoid (32: 0 [right arrow] 1, only occurring independently in a few taxa outside this clade C38 and only reverted, inside of it, in cypriniforms; the condition of [dagger] Santanichthys diasii and of [dagger] Clupavus maroccanus is not clear).
Nasal cavity extending medially, separated from contralateral structure by thin ventromedian lamina of mesethmoid. Accessory nasal sac located medial to anterior infraorbitals.
Frontal contacting mesethmoid but not lateral ethmoid.
inermis: "Cranium rather thin; interorbital space and occiput plain or very slightly convex, the former about 3.0 times in base of the cranium; preocular spines always present; supraocular and parietal spines small or absent; postocular, tympanic and nuchal spines entirely absent; cranial ridges absent except for the parietal which is very low and sometimes scaled over; parietals widely separated; mesethmoid processes depressed or slightly directed upward; base of cranium strongly curved; ventral process of basisphenoid feeble; nasal spines low, but strong.
pachycephalus: "Cranium very thick and heavy; interorbital space deeply concave, about 3 1/2 in base of cranium; cranial spines broad and stout, the pointed tips directed backward; preocular, postocular, tympanic and parietal spines present; supraocular, coronal and nuchal spines absent; supraocular ridges exceedingly high and stout, forming a narrow flat area between them; frontal ridges barely evident, can not be seen without elimination of the skin; parietal ridges broad and high, but a little lower than the supraocular ridges; nasal spines stout, directed upward and slightly backward; mesethmoid processes strongly compressed, directed forward and upward; parietal bones separated; base of cranium straight; ventral process of basisphenoid entirely meeting the parasphenoid.
Mesethmoid cartilage lacking extension to dorsal and lateral margins of rhinosphenoid, but with cartilage along dorsal and anterior margin of parasphenoid.
Mesethmoid cartilage extending to anterior limit of parasphenoid.
[0] Does not situate well posteriorly to anteroventral margin of mesethmoid (or of supraethmoid and/or rostrodermethmoids: see above) (e.g.
Anterolateral processes of mesethmoid (or of supraethmoid and/ or rostrodermethmoids) supporting and/or articulating with premaxillae.
The ethmoid cartilage, situated ventrally to both the lateral ethmoid and the mesethmoid, is well-developed, with its anterior portion being markedly extended anteriorly and almost reaching the posterior surface of the premaxillaries.
Five synapomorphies are commonly listed in catfish literature to support the monophyly of the subfamily Heptapterinae, namely: 1) "posterior limb of fourth transverse process laterally expanded above swimbladder and notched once to several times"; 2) "neural spines of Weberian complex centrum joined by a straight-edged, horizontal or sometimes sloping bony lamina"; 3) "process for insertion of levator operculi muscle on posterodorsal corner of hyomandibula greatly expanded"; 4) "quadrate with a free dorsal margin and bifid shape, its posterior and anterior limbs articulate separately with hyomandibula and metapterygoid"; 5) "presence of an anteriorly recurved process drawn out from ventrolateral corner of mesethmoid" (Lundberg et al., 1991: 198-199).
larnaudii; 3) there are no dorso-medial concavities of the mesethmoids; 4) the autopalatines exhibit, anterodorsally to their articular surface for the neurocranium, a prominent, dorsally pointed, triangular process; 5) the 'elastic spring apparatus' is missing; 6) the parurohyals are significantly smaller than those of P.