umbo

(redirected from umbonal)
Also found in: Dictionary, Thesaurus, Encyclopedia.

umbo

 [um´bo] (L.)
1. a rounded elevation.
2. the slight projection at the center of the outer surface of the tympanic membrane.

um·bo

, gen.

um·bo·nis

, pl.

um·bo·nes

(ŭm'bō, -bō-nis, -bō-nēs),
1. A projecting point of a surface.
2. Umbo of tympanic membrane.
[L. boss of a shield, a knob]

umbo

/um·bo/ (um´bo) pl. umbo´nes   [L.]
1. a rounded elevation.
2. the slight projection at the center of the outer surface of the tympanic membrane.

umbo

(ŭm′bō)
n. pl. umbos or umbones (ŭm-bō′nēz)
A small anatomical projection on a surface, such as that on the inner surface of the eardrum at the end of the manubrium of the malleus, corresponding to the most elevated point of the eardrum.

um′bo·nal (ŭm′bə-nəl, ŭm-bō′nəl), um·bon′ic (ŭm-bŏn′ĭk) adj.

umbo

Etymology: L, knob
a projection on any rounded surface, such as the inner surface of the tympanic membrane where the malleus is attached.

um·bo

, pl. umbones (ŭm'bō, -nēz) [TA]
1. A projecting point of a surface.
2. [TA]
Synonym(s): umbo of tympanic membrane.
[L. boss of a shield, a knob]

umbo

the pointed centre of a clam shell, being the oldest part around which are many concentric lines of growth.

umbo 

An area (0.15 mm-0.20 mm) in the centre of the foveola. Stimulation of this area results in the highest visual acuity.

umbo

pl. umbones [L.] a round projection.

umbo membrana tympanae
the slight projection at the center of the outer surface of the tympanic membrane.
References in periodicals archive ?
Numerous ridges radiate from the umbonal area and are crossed by fainter comarginal ridges on the right valve.
The composite mold from the black shale unit has a much stronger convexity of the ventral margin, a less produced anterior margin, and less strongly sloping umbonal ridge than the limestone mold or in S.
0 mm high, with a relatively strong posterior umbonal ridge extending towards the posteroventral margin.
Shell with strongly sloping dorsoposterior margin meeting short posterior margin with an obtuse angle; anterior margin convex; ventral margin flatly convex; valves angulated from umbonal area to ventroposterior margin; area dorsal to angulation concave; beaks tightly incurved near anterior margin, prosogyrate; lunule and escutcheon not deeply impressed; comarginal ridges become coarser during growth with equal-sized interspaces, eight in 2 mm near ventral margin; internal features not observed.
subplana Hall, 1858a, differs by being more narrowly elongate with a less produced umbonal region and E.
Small Sanguinolites with nearly parallel dorsal and ventral margins; umbonal shoulder rounded; ornamentation of strap-like, comarginal ridges.
Small, narrow, elongate, subtrapezoidal shell; anterior margin narrowly convex, extended; dorsal and ventral margins nearly parallel; posterior margin truncate, flatly convex; beaks near anterior end, tightly incurved, prosogyrate; lunule and escutcheon present; umbonal ridge rounded, extending to ventoposterior margin; anterior and ventral area below umbonal ridge with numerous strap-like, comarginal growth ridges having steep edge dorsally; other features not preserved.
naidiformis, both by Winchell, 1870, by having more uniform ornamentation and a rounded umbonal ridge.
andrewsi in having less pronounced and less regularly distributed comarginal plicae, the beaks are located further from the anterior margin, and the posterior umbonal shoulder is weaker.
Medium-sized, gibbous shell; dorsal and ventral margins subparallel; ventral margin broadly convex; anterior and posterior margins subequally convex; beaks located one-third length posterior to anterior margin, incurred, prosogyrate; lunule and escutcheon not visible; broad, shallow sulcus extending from umbonal area to ventral margin posterior to midlength; surface with numerous closely-spaced, comarginal ridges with two to four finer ridges between coarser ridges; internal features not observed.
Regression analyses did not reveal any significant relationships for umbonal stages ([R.
Larvae that had only reached umbonal stage on Day 15 were smaller and were less likely to metamorphose than larvae that had reached pediveliger stage on Day 15 (Fig.