triangle 
hounded above by the lower margin of the lower jaw. and 
on its other two sides by the digastric muscle. See cut 
under mutdei. Suboccipital triangle, a triangle on 
the surface of the neck bounded by the anterior border of 
the trapezius. the sternoclidomastoid, and the omohyoid 
muscle. See cut under mtMcfei. Superior carotid tri- 
angle, a triangle on the surface of the neck bounded 
bythe sternoclidomastoid, omohyoid, and digastric mus- 
cles. Also called triangle of election, with reference to 
facilities afforded for tying the carotid. See cut under 
in *!. Supplemental triangle, a spherical triangle 
formed by joining the poles of three great circles. 
Surgical triangle, a triangular space, area, or region 
containing important vessels and nerves which may re- 
quire to be operated upon : chiefly said of several such 
regions of the neck. Triangle Of election, in aarg., 
same as superior carotid triangle. Triangle of forces, 
a name given to the proposition in statics which asserts 
that, if three forces meeting at a point in one plane be in 
equilibrium, and if on that plane any three mutually in- 
tersecting lines be drawn parallel to the directions of the 
three forces, a triangle will be formed the lengths of whose 
sides will be proportional to the magnitudes of the forces. 
Triangle Of Hesselbach. See Uesselbachian Mangle. 
Triangle Of necessity, in surg., the inferior carotid 
triangle, where the artery must be tied, if there be no room 
for choice or election. Triangle Of Petit, a triangular 
space in the lateral wall of the abdomen, bounded below 
by the crest of the ilium and laterally by the oblhjuus ex- 
ternus and latissinvus dorsi muscles. Triangle of ref- 
erence. Same as fundamental triangle. Triangles to. 
cross, in her., a bearing consisting of a number of trian- 
gles arranged in a cross, the number being specified in the 
blazon. Also called cross of triangles. Triangles of the 
neck, certain triangular spaces or areas on each side of the 
neck, bounded by several muscles, notably the sternocli- 
domastoid, omohyoid, and digastricus, and by the collar- 
bone and lower jaw-bone, and containing important ves- 
sels and nerves which may require to be operated upon. 
The sides of all these triangles are the natural landmarks 
in the topographical anatomy of the neck, Triangle spi- 
der, a spider, as Hyptiotes camtus, which spins a triangu- 
Triangle Spider {Hyptiotes cavatus). 
(Spider five times natural size, web one third natural size.) 
lar web in trees, which it sets like a net, capable of being 
sprung upon its prey by letting go one of the elastic threads 
which the spider holds. Vertical triangle, in entom., a 
triangular space on the vertex, formed by the eyes when 
they meet in front, as in many Diptera. Vesical tri- 
angle, the trigonum of the bladder. 
triangled (tri'ang-gld), a. [< triangle + -ed 2 .] 
1. Having three angles; having the form of a 
triangle; also, belonging to or situated in a 
triangle. 
The forme or situation of this Citty is like vnto a Tri- 
angle. ... In one of these triangled points . . . stand- 
eth the Pallace of the Great Turke, called Seralia. 
W. Lithgour, Travels, iv. 
2. In her., divided into triangles: noting the 
field, and equivalent to harry bend;/ dexter and 
sinister, or paly bendy dfjrter and sinister. 
triangular (tri-ang'gu-lar), a. [= F. triangu- 
laire = Pr. triangular =" Sp. Pg. triangular = 
It. triangolare, < LL. triangularis, < L. triangu- 
lus, three-cornered, triangulum, a triangle: see 
triangle.] 1 . Of or pertaining to a triangle ; 
consisting of a triangle. 2. Three-cornered 
and three-sided; included within three sides 
and angles : as, a triangular plot of ground ; a 
triangular building. Specifically, in bot. and zooi. : (a) 
Flat or lamellar and having three sides : as, a triangular 
leaf. (6) Having three lateral faces and edges; triangular 
iti cross-section ; trihedral : as, a triangular stem, seed, or 
column. 
3. Hence, of or pertaining to three independent 
things ; three-sided as regards elements, inter- 
ests, or parties: as, a triangu- 
lar treaty. 
The same triangular contest be 
tween the three Henrys and their 
partizans. 
Motley, Hist. Netherlands, II. 135. 
4 In her., represented as solid 
and three-sided: thus, a tri- 
angular pyramid or a triangu- 
lar pyramid reversed is a point 
or a pile which is divided by 
a line indicating a projecting 
ed|*e, and is treated as if a 
solid seen in perspective. 
Triangular COmpaSS, a compass Triangular Compass. 
6464 
having three legs, two opening in the usual manner, and 
the third turning round an extension of the central pin 
of the other two, besides having a motion on its own cen- 
tral joint. By means of this instrument any triangle or 
any three points may be taken off at once. Triangular 
coordinates. See coiirdi nate. Triangular crab, any 
maioid, whose carapace is more or less triangular. See 
Triamjiilares. Triangular fascia, a thin triangular 
fibrous band reflected upward and inward beneath the 
spermatic cord from the attachment of Gimbernat's liga- 
ment on the linea iliopectinaja to the linea alba. Also 
called triangular ligament. Triangular fibrocarti- 
lage, file, fret. See the nouns. Triangular level, a 
light frame in the shape of the letter A, 
and having a plumb-line which deter- 
mines vertically. Triangular liga- 
ment, (a) Same as triangular Jama. 
(b) A dense fibrous membrane stretched 
across the subpubic arch on the deep 
surface of the crura of the penis and the 
bulb of the urethra. Also called deep Triangular Level. 
perineal or subpubic fascia. Triangu- 
lar numbers, the series of flgurate numbers which con 
sists of the successive sums of the terms of an arithmeti- 
cal series whosefirst term is 1 and the common difference 1. 
Thus, 1, 8, 6, 10, 15, 21, 28, etc., are triangular numbers. 
They are so called because the number of points expressed 
by any one of them may be arranged in the form of an 
equilateral triangle. Triangular plexus. See plexus. 
Triangular pyramid, a pyramid whose base is a tri- 
angle, its sides consisting of three triangles which meet 
in a point called its vertex. Triangular scale. See 
scales. 
triangulare (tri-ang-gu-la're), n. ; pi. triaiii/tt- 
laria (-ri-a). [NL. (so. os, bone), neut. of L. 
triangularis : see triangular.] A peculiar bone 
of the tarsus of some animals, as Cryptoprocta 
ferox: more fully called triangulare tarsi. Bar- 
dcli'ben. 
Triangulares (tri-ang-gu-la'rez), n. pi. [NL., 
pi. of L. triangularis: see triangular.] A group 
of crabs, the maioids or spider-crabs, of more 
or less triangular figure. See cuts under Oxy- 
rliyncliit, Leptopodiits, and spider-crab. 
triangularis (tri-ang-gu-la'ris), n. ; pi. trian- 
gulares (-rez). [NL. (sc. wusevlus, muscle): 
see triangular.] In anat.: (a) A triangular 
muscle of the thorax, on the inner surface of 
the front of the chest, under the sternum and 
parts of several ribs : more fully called triangu- 
laris sterni. Also sternocostalis. (b) The tri- 
angular muscle of the chin ; the depressor an- 
guli oris: more fully called triangularis menti. 
See cut under muscle^. 
triangularity (tri-ang-gu-lar'i-ti), w. [< tri- 
angular + -ity.] The state or condition of be- 
ing triangular; triangular form. 
triangularly (tri-ang'gu-lar-li), adv. In a tri- 
angular manner ; after the form of a triangle. 
triangularyt (tri-ang'gu-la-ri), a. [< L. trian- 
gularix, three-cornered: see triangular.] Tri- 
angular. 
Lifting up in the upper part of the skull the two trian- 
gulary bones called sincipital. 
Urguhart, tr. of Kabelais, i. 45. 
triangulate (tri-ang'gu-lat), r. t. ; pret. and pp. 
triangulated, ppr. triangulating. [< NL. *tri- 
angulatus, pp. of * triangulare, < L. triangulus, 
three-cornered, triangular : see triangle.'] 1 . To 
make three-cornered or triangular. Imp. Diet. 
2. In snrv., to divide into triangles; survey 
by dividing into triangles of which the sides 
and angles are measured. 3. To determine or 
observe trigonometrically ; study by means of 
triangulation : as, to triangulate the height of a 
mountain. 
Before each shot flag signals were exchanged with ob- 
servers on shore, who triangulated the range. 
Set. Amer., N. 8., LVII. 214. 
triangulate (tri-ang'gu-lat), a. [< NL. *trian- 
gulatus: see the verb.] In rooV., composed of 
or marked with triangles. A triangulate bar isgen- 
erally formed of triangles with their bases together, so 
that the angles touch and sometimes coalesce ; it is a form 
of ornamentation common on the wings of Lepidoptera. 
triangulately (tri-ang'gu-lat-li), adr. Inzoo'l., 
so as to form triangles : as, a margin or surface 
marked triangulately with black that is, hav- 
ing triangular black marks. 
triangulation (tri-ang-gu-la'shqu), w. [= F. 
triangulation; as triangulate -f- -ion.] 1. A 
making triangular; formation into triangles. 
2. The operation and immediate result of 
measuring (ordinarily with a theodolite) the 
angles of a network of triangles laid out on 
the earth's surface by marking their vertices. 
The triangulation usually* proceeds from a base-line, the 
measurement of which is necessary, though no part of the 
triangulation proper. The geographical positions of the 
extremities of this base having been ascertained, and the 
triangulation, or operation of measuring the angles, hav- 
ing been completed, by trigonometrical calculations called 
the reduction of the triangulation (commonly involving a 
process of distributing the errors by least squares, called 
the adjustment of the triangulation) the geographical posi- 
tions of all the other vertices are calculated, assuming the 
figure of the earth to be known. By the combination of 
Triassic 
the triangulations of different countries the figure of the 
earth is ascertained. See cut under base-line. 
triangulator (tri-aiig'Kfi-lri-tor), n. [< triangu- 
late + -wl.] One who performs the work of 
triangulation in a trigonometrical survey. 
trianguloid (tri-ang'gu-loid), a. [< L. triinigii- 
lum, a triangle, + Gr. fWof, form.] Somewhat 
triangular in shape. 
A trianguloid space. //. Kpe.nc.fr. (Imp. Diet.) 
Triangulum (tri-ang'gu-lum), n. [L.: see tri- 
angle.] An ancient northern constellation in 
the form of the letter delta (A). It has one star 
of the third magnitude Triangulum Australe 
(the Southern Triangle), a southern constellation, added 
by Petrus Theodori in the fifteenth century, south of Ara. 
It contains one star of the second and two of the third 
magnitude Triangulum Minus (the Lesser Triangle), 
a constellation introduced by Hevelius in 1690, immedi- 
ately south of Triangulum. It is no longer in use. 
triantelope, triantulope (tri-an'te-lop, -tu- 
16p), n. [A corruption of tarantula, simulating 
iinli'liijii'.] A tarantula. [Australia.] 
Tarantulas, or large spiders (as the bushmen call them, 
triantiilopes), . . . come crawling down the sides of the 
tent in wet weather. 
Bush Wniiili fhi'js ttj'a Naturalist, p. 208. 
Trianthema(tri-au-the'ma), . [NL. (Linnseus, 
1753), < (jr. rpe'if (rp/-), three, + arOr/ua, a flower- 
ing, < aifa/v, flower, < arflof, a flower.] A genus 
of plants, of the order t'ieoidctf and tribe Ai:n- 
idcse. It is distinguished from the related genus Sesuviutn 
by its stipulate leaves, and ovary with one or two cells. 
There are 12 species, scattered through warm parts of 
Asia, Africa, and Australia, with one American species, T. 
monogunum, native from Cuba to Venezuela and the Gala- 
pagos Islands. They are usually diffuse prostrate herbs, 
with opposite, unequal, entire leaves, and two-bracted 
flowers without petals, but with the five calyx-lobes col- 
ored within. T. monogunum is known in Jamaica as horse- 
purslane. 
trianthous (tri-an'thus), a. [< Gr. T/orif (T/M-), 
three, + av6o(, a flower.] In bot., three-flow- 
ered. 
triantulope,". See triantelope. 
triapsal (tri-ap'sal), a. [< L. tres (tri-), three, 
+ apsis, apse, + -al.] Same as triapsidal. 
There is, so far as I know, only one triapsal church, that 
of St. Croix at Mont Majour near Aries. 
J. Fergusson, Hist. Arch., I. 462. 
triapsidal (tri-ap'si-dal), a. [< L. trcs (tri-), 
three, + apsis (apsid-}, apse, + -al.] Having 
three apses ; subdivided into three apses ; char- 
acterized by a triple arrangement of the apse, 
as most Greek churches. 
The arrangement of the triapsidal basilica is perfect. 
E. A. Freeman, Venice, p. 131. 
triarch (tri'ark), a. [< Gr. Tpiapxof, having 
three rulers, fig. having three branches, as a 
horn, < rptif (TP'-), three, + apxAc,, ruler.] In 
bot., noting radial fibrovascular bundles hav- 
ing three rays. Kastin. 
triarchee (ti-i-ar'che), a. [Heraldic F., as tri- 
+ arch + -eel.] In her., treble-arched ; having 
three arches : noting a bridge or the like. 
triarchy (tri'iir-ki), . ; pi. triarchies (-kiz). [< 
Gr. rpiapx'ia, government by three, a triumvir- 
ate, < Tpeif (rpi-), three, + apxetv, rule.] Rule 
by three persons ; a three-headed government. 
She [the rational soulj issueth forth her commands, and, 
dividing her empire into a triarchy, she governs by three 
viceroys, the three faculties. 
Homll, Parly of Beasts, p. 143. (Dames.) 
triarian (tri-a'ri-an), a. [< L. triarii, soldiers 
of the third rank or class (< tres, tri-, three), + 
-an.] Occupying the third post or place in an 
array. 
Let the brave Second and Triarian band 
Firm against all impression stand. 
Coicley, Restoration of K. Charles II. 
triarticulate (tri-ar-tik'u-lat), a. [< L. tres 
(tri-), three, -f- articulatus, jointed: see articu- 
late.] In zool. and anat., composed of three 
joints or articles : as, a triarticulate palpus ; our 
fingers are triarticulate. Also triarticttlated. 
trias (tri'as), w. [NL., < LL. trias, < Gr. Tptd(, 
the number three: see triad.] 1. In music, 
same as triad, 3. 2. [.cap.] In geol., same as 
Triassic. 3. [cap.] In German Jtist., a name 
sometimes given to the old German empire, 
reckoned as consisting of three coordinate 
parts Austria, Prussia, and the group of 
smaller states. 
Triassic (tii-as'ik), a. and . [= F. triasique = 
Sp. tridxico; as trias + -ic.] In geol., the lower 
of the three great divisions of the entire sys- 
tem of fossiliferous rocks (Triassic, Jurassic. 
Cretaceous) which together make up the Meso- 
zoic or Secondary series. The Triassic lies above 
the Permian, and beneath the Jurassic. The threefold 
subdivision from which the Triassic derives its name is 
best seen in central Europe, and especially in northern 
Germany, where the bunter-sandstein, muscht-lkalk, and 
