Also found in: Medical, Encyclopedia.


n.1.(Anat.) The inferior and posterior of the three elements forming the periotic bone.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
However, Hampe (1992) justifies its provisional inclusion of the specimen in the genus Kronosaurus based on the large size of the skeleton, the short neck with 12 vertebrae, the expanded opisthotic, the small and unpaired supraoccipital, and the cervical rib facets extending through the entire length of the centra.
It articulates with the skull in two distinct places: 1) through the external optical process (Capitulum squamosum), supported in the ventro-caudal facet of the zygomatic process and 2) by the internal optical process (Capitulum oticum) that articulates with the cotyla quadrdtica and otici of the pro-optical and opisthotic bones, processes of homogeneous configuration amongst the species.
The absence of palatal contact of the vomer with the pterygoids and the presence of a ventral ridge on the opisthotic, being developed an enclosed middle ear region, are not shared with the clade Plesiochelyidae.
Most of the bones (supraoccipital, epitotic, pterotic, opisthotic, parietal, etc.) that compose the posterior part of the neurocranium are crushed beyond recognition.
They diagnosed the subgenus Mesoclemmys largely on morphological characters: small chin barbels (=barbels); the presence of zero to five often discontiguous neural bones, never contacting the nuchal (proneural) bone; less than thirty cm in shell length; a small head, pointed anteriorly as in Batrachemys; posteriorly wide hourglass-shaped parietals as in Phrynops; and parieto-squamosal arches that pass directly above the opisthotics. For the subgenus Batrachemys, Pritchard and Trebbau used the following characters: zero (often) to five neural bones present, never contacting the nuchal bone; comparatively short barbels; broad head; narrow, parallel-sided parietals; and slender parieto-squamosal arches located posterior to the rear margin of the opisthotic bones.
a, angular; art, articular; bo, basioccipital; d, dentary; ect, ectopterygoid; f, frontal; j, jugal; l, lacrimal; mcg, meckelian groove; mx, maxilla; n, nasal; op, opisthotic; p, parietal; pal, palatine; pf, postfrontal; pmx, premaxilla; po, postorbital; pp, postparietal; pro, prootic; prf, prefrontal; pbs, parabasisphenoid; pt, pterygoid; q, quadrate, qj, quadratojugal; so, supraoccipital; sp, splenial; sq, squamosal; st, supratemporal; sa, surangular; ta, tabular; v, vomer