thoracic 
vertebra which hears functional ring; entering into the 
fi>rm:itlon of the thorax: >pn-iti*:.illy imtinn surh vt-rtv- 
bne (all vertebra being ilnraul in one sense), (c) Pertain- 
iiiK to the Ill-mi ;n ii I i lii>i;ix of some ammaN ; < t'plKilothn- 
racIc: as, tht/racic appendages, (d) Att;ielu-<l to tin; tho- 
rax : as, thoracic limbs or appendages; the thoracic girdle 
(that is, the pectoral iirch, or ihoulder-giMl* of ii \rrh- 
hrnti-i: jHvton.l in pi^ition, as the ventral fins of some 
H-|M . (-) Pertaining to the I'mnt ;ind sides of the thorax 
"i tn the breast; pectoral: as, the mammary glands of 
111:111 an; thtinu'ic. </) Done <u effeutt-d by means of the 
thorax : as. th"fi,-i,- n^|iiraiinu. <//> Atffcting the thorax 
oriNoivuim: as, Moractc diseases, symptoms, or remedies. 
2. Having a thorax (of this or that kind); be- 
longing to tin- Tlmftti-irti: ;is, tlir thmwic cirri- 
peds. 3. Having the ventral fins thoracic in 
position; belonging to the Thordciri : as, a tho- 
rttt'ic fish. -Thoracic angles, the cornereof the thorax, 
or of the prothorax in insects with wing-covers. Thoracic 
aorta, that section of the aorta which traverses the cavity 
of the thorax. It extends from the origin of the vessel to its 
passage through the aortic orifice of the diaphragm, where 
it becomes the abdominal aorta. The term is also restricted 
to the straight or descending part of the aorta (excluding 
the arch). In this sense the tnoracic aorta begins where 
the arch ends, about opposite the fifth thoracic vertebra. 
The branches of the thoracic aorta are the pericardia!, 
bronchial (the nutrient vessels of the lungs), esophageal, 
postmediastiual, and the usually ten pairs of intercostals. 
SrtM uts under diaphragm and thorax. Thoracic artery, 
one of several branches given off by the axillary artery in 
the second and third sections of its course, and distributed 
chiefly to the pectoral muscles and adjacent soft tissues. 
Four such vessels are named in man as the superior, aero- 
mial, long, and alar. They are also called suprathoracit, 
acromiothoracic or thoracacromial or thoracico-acromial, 
loHtfithoracic, and alithwacic. Thoracic axis, the com- 
mon trunk of the acromiothoracic and superior thoracic 
arteries, when these are given otf together. Thoracic 
duct. See duct, and cut under diaphragm, Thoracic 
ganglia. See ganglion. Thoracic girdle, the pectoral 
girdle, or scapular arch. See cuts under epipleura, omonter- 
num, and sternum. Thoracic grooving, the longitudi- 
nal depressions along the sternum on either side in rachitic 
or pigeon-breasted children. Thoracic index, the ratio 
between the a ntero- posterior and transverse diameters of 
the thorax. Thoracic limbs, the fore limbs of a verte- 
brate ; the arms of a man, fore legs of a quadruped, wings 
of a bird, pectoral fins of a fish; the appendages of the scap- 
ular arch, or shoulder-girdle; in invertebrates, the appen- 
dages proper to the thorax, generally the ambulatory and 
chelate, as distinguished from abdominal appendages, 
mouth-parts, etc. 8ee cut under Aranrida. Thoracic 
nerves, (a) Anterior thoracic, two branches, the external 
and internal, arisingfrom the outer and inner cords of the 
brachlal plexus and distributed to the pec to rales muscles. 
(b) Posterior thoracic, a branch from the upper two or three 
nerves of the brachial plexus, passing on the side of the chest 
to be distributed to the serratus magnus. Also called long 
thoracic, and external respiratory nerve of Bell. Thoracic 
parietes, the walls of the chest; especially, the mova- 
ble front and sides of the chest, whose bony basis is the 
ribs and sternum. Thoracic region, (a) The extent 
or superficies of the thorax as a part of the body; some 
part of the thoracic walls, with reference to groups of 
muscles which lie upon them : as, the anterior or lateral 
thoracic region. (b) Especially, one of the several parts 
Thoracic Regions, bounded by thick black lines, 
r, r, right and left humeral ; a, 2, right and left subclavian ; 3, 3. 
right ana left mammary; 4, 4, right and left axillary ; 5, 5, right and 
left suhaxillary or lateral ; 6, 6, right and left scapular ; 7, 7, right 
and left mtcrscapnl.ir ; 8, 8. right and left superior dorsai, or sub- 
scapular. The viscera of the thorax are indicated by dotted lines 
tf, diaphragm ; #, heart; r, lungs; rf, liver; t, kidneys ,f, stomach. 
into which the surface of the human thorax is divided or 
mapped out by certain imaginary lines, which to some 
extent denote the situation of the contained viscera, and 
thus serve for medical and surgical purposes. These re- 
gions, unlike some of the corresponding abdominnl re- 
gions, are all In pairs (right and left), in one nomenclature 
known as the humeral, stiMavian, mammary, axillary, 
scapular, iHterscapular, and ntbscapular. Thoracic re- 
gion Of the spine, that portion of the spine which is com- 
posed of thoiMrir vfitrhnc. Also called dorsal region. 
Thoracic shield, one of the three plates covering the 
thoracic rings in insect larvte. Thoracic vertebra, any 
vertebra which bears a developed rib entering Into the 
formation of a thorax. Also called dorsal vertebra. ThO- 
raclc viscera, the viscera contained within the cavity 
of the thorax namely, the heart, lungs, thymus, a sec- 
tion of the esophagus, thoracic duct, thoracic aorta, caval 
veins, and other large vessels. Transverse thoracic 
furrow, in many Diptera, "a suture crossing the meso- 
tborax and ending on each side a little before the base of 
the wing : its presence or absence, and form, are important 
characters in classification " (Oaten Sacken). 
II. n. 1. A thoracic structure: rsp<>riully. a 
thoracic artery or nerve, or a rib-bearing dor- 
sal vertebra. 2. A thoracic lish. 
Tuoracica(tho-ras'i-kii). ;/./)/. [XL., ueut. pi. 
of *thorarifii.f : see llinracif.] The principal 
group of the ('irrii>rdi<i, by some recogni. 
6290 
an order, consist ing of the ordinary Beguile and 
peilunculated cirripeils, or barnacles and acorn- 
shells, in which the abdomen is rudimentary 
and there are six thoracic segments with as 
many pairs of cirrone limbs. See Cirri/mlm. 
1.1 JHIS. lilllflllllX. 
thoracicabdominal, thoracicacromial, ". 
Same as t/ioracabdominal, thorararrniiiinl. 
Thoracicit (tho-ras'i-si). . pi. [NL., pi. of 
'thoraciciut: see thoracic.] In ichth., the third 
one of four Linnean orders of fishes (the others 
being Ajxiilin, Jiii/iiln rex, .lliitomiHiilfxi, charac- 
terized by the thoracic position of the ventral 
fins, which are placed beneath the pectorals. 
By Cuvier and others the term has been recognized with 
various limitations, but It Is no longer used in classifying 
Ashes, though the adjective thoracic remains as a descrip- 
tive terra In its original sense. 
thoracico-acromialis (th^-ras'i-ko-a-kro-mi- 
a'lis), n. ; pi. thoracico-acromiales (-lez). [X 1 .. . 
< "thoracicus, thoracic, + acromialis, acromial.j 
The acromiothoracic artery, a branch of the 
axillary, given off just above the pectoralis mi- 
nor, and dividing into three sets of branches. 
thoracicohumeral (tho-ras'i-ko-hu'me-ral), a. 
[< NL. "thoracicus, thoracic, + humeraliis, hume- 
ral.] Pertaining to the thorax and the hume- 
rus. or to the chest and the upper arm. 
thoracicohumeralis (tho-ras'i-ko-hu-me-ra'- 
lis), n. ; pi. thoracicohumerales (-lez). [NL.: 
see thoracicohumeral.] An artery, a branch of 
the thoracico-acromialis, which descends upon 
the arm with the cephalic vein in the interval 
between the great pectoral and deltoid muscles. 
thoraciform (tho-ras'i-fdrm), a. [< L. thorax 
(thorac-), the thorax, + forma, form.] In en- 
tom., noting the mesonotum when it is very 
large and forms the main part of the upper 
surface of the thorax, as in Diptera and most 
Hymenoiitera. 
thoracipod (tho-ras'i-pod), a. and . [< L. 
thorax (thorac-), the thorax, + Gr. iroif (TTOO-) = 
E.foot.] I. a. Having thoracic limbs differen- 
tiated as ambulatory legs, as a crab or lobster; 
belonging to the Thoracipoda; malacostracous. 
II. n. A member of the Thoracipoda; a 
crustacean which walks on specialized thora- 
cic limbs (pereiopods); a malacostracan. 
Thoracipoda (tho-ra-sip'o-da), n. pi. [NL. : 
see thoracipod.] In some systems, a subclass 
or superorder of Crustacea corresponding to 
Malacostraca; the higher series of crustaceans, 
contrasted with the entomostracans or Gna- 
thopoda. The name refers to the fact that, the seven 
anterior or cephalic segment* being specialized for sensa- 
tion and nutrition, the next or thoracic segments distinc- 
tively subserve locomotion. The name is proposed as a 
substitute for Malacotfraca. Encyc. Brit., VI. 655. 
thoracipodous (tho-ra-sip'o-dus), a. [< tho- 
racipod + -OKA.] Same as thoracipod. 
thoracispinal (tho-ras-i-spi'nal), a. [< L. tho- 
rax (thorac-), the thorax, + snina, spine: see 
spinal.] Of or pertaining to tne thoracic sec- 
tion of the spinal column: as, a thoracispinal 
nerve. Coues. 1887. 
thoracodidymus (tho-ra-ko-did'i-mus), n. ; pi. 
thoracodidymi (-mi). [NL., < Gr. 8upa (BupaK-), 
thorax, + iiovfior,, double.] In teratol., a double 
monster the two bodies of which are joined at 
the thorax. 
thoracogastr odidymus (tho - ra - ko - gas - tro- 
did'i-mus), n.; pi. thoracogastrodidymi (-mi). 
[NL., < Gr. 96paf (6upax-), thorax, + yaorf/p, 
stomach, + iiiv/iof, double.] In teratol., a dou- 
ble monster with united thoraces and abdomen. 
thoracometer (tho-ra-kom'e-ter), n. [< Gr. fti- 
paf (BupaK-), the thorax, + fitrpav, measure.] An 
instrument for measuring the range of respira- 
tory movement of any point in the thorax. 
thoracopagUS (tho-ra-kop'a-gus), n. ; pi. thorn- 
copagi (-JI). [NL., (. Gr. 6apaf (0U/MK-), the tho- 
rax, -I- mi) of, that which is firmly set.] In tera- 
tol., a double monster with more or less fusion 
of the thoraces. 
thoracoplasty (tho-ra'ko-plas-ti), w. [< Gr. 
6uoaf (Oupan-), thorax, + v/.aaotiv, put in a cer- 
tain form.] Removal of a section of one or 
more ribs for the cure of a fistula of the chest- 
wall following empyema. 
Thoracostraca (tho-ra-kos'tra-kS), n.pl. [NL., 
< Gr. ftipof (Oupan-), the thorax, + oarpaKOi; a 
shell.] In some systems, a division of mala- 
costracous crustaceans, including the podoph- 
thalmous or stalk-eyed crustaceans, as crabs, 
shrimps, prawns, and lobsters: nearly conter- 
minous with l'i>ilojihtli<i/ina. 
thqracOStracOUS (tho-ra-kos'tra-kus), ii. Per- 
taining to the Tlioriii-iixiriica. 
thorax 
thoracotheca (tho-ra-ko-tlie'kii i. .: pi. tkora- 
eotii0em(-Mti). [NL.,<Grr.ft -). the tho- 
rax. + //,(,/,, a MM. 1 In niliiin.. the truiik-oase 
of a pnpn, or that part of t he integument which 
covers the thorax. Al-o i-ifintheea, 
thoracotomy (tho-ni-kot'o-mi), n. [< Gr. Oupal- 
(HufMt,-), the thorax, + -rn/iin, < ftuvttv, ra/Jiii', 
cut.) In ><./.. 111.- operation of free incision 
through the llionicic walls. Compare t/i-i, 
tuli. 
thorah, . See tornh. 
thoral (tho'ral), ii. (Prop, toral, < L. torn*, 
ML. erroneously tlmrux. a cushion, couch, bed: 
see torus.] Of or pertaining to the marriage- 
bed; nuptial; specifically, in palmiatri/, noting 
the line or mark of Venus on the hanu. 
thorax (tho'raks), M.; pi. thoraces (th^-ra'sSz). 
[< L. thorns (thoriic-), < (ir. tiupaf (Oupan-), a 
breastplate, also the part of the body covered 
by the oreastplate, the thorax.] 1. Inaiiat. and 
:i>iil.. a part of the trunk between the head or 
neck and the abdomen or tail, in any way distin- 
guished, as by containing the heart and lungs, 
by being inclosed with large ribs, or by bear- 
ing certain limbs not borne elsewhere. The name 
Is applied both to the walls and to the cavity of this 
part of the body, but not to the contents of the cavity, uid 
properly not to the thoracic appendages. In all verte- 
brates the thorax represent* several of the segments or 
somites of the body succeeding the cervical and succeeded 
by the abdominal or pelvic segments. It is generally de- 
nned by the elongation of several rilw and the connection 
of some or most of these with a breast-bone, the thoracic 
skeleton thusform- 
SC 
/ /' 
Ing a bony cage or 
frame which con- 
tains and defends 
the principal or- 
gans of circulation 
and respiration. In 
Invertebrates, how- 
ever, the thorax Is 
defined upon other 
considerations, (a) 
In man and all 
mammals the tho- 
rax Is sharply 
U 
marked off from 
the rest of the 
trunk by the lack 
nv 
Cross-section of Human Chest Tiewed from 
above, showing heart, lungs, and great res 
sels in place. Each lung is invested with 
of deve'loned cer- pleura and the heart with pericardium : the 
A )iK.,>.r dark borders around the lungs aivl heart are 
lumbar c4 j Ue . , pkura and of pericardium ; Ihe 
interval between pleural cavities of oppo- 
site sides is the mediastinum ; the anterior 
mediastinum is entirely black ; the middle 
is occupied by the heart, the posterior by the 
ribs, and IU cav- 
ity is completely 
shut off from that 
of the abdomen 
by the diaphragm. 
The human thorax 
Is of conical figure, 
somewhat like the 
esophagus, etc 
XL, right lung; LI., left lung; RP and 
LP, two pulmonary veins; PA, pulmonary 
artery branching to each lung ; Ae, ascend- 
ing part of arch of aorta ; Ac' , descending 
aorta (intervening arch of aorta cut away) ; 
frustum of a cone, the line from Ao rests upon heart ; SC, 
supe- 
d left 
bronchi, cut end of each presenting : <E, 
T, body of a too- 
narrowed above, nor vena cava : Br and Br, right and I 
lim-iit hotnw rf bronchi, cut end of each j 
. & sSfeSi?*' 
depth, and in 
cross-section somewhat cardiform or heart-shaped, from 
the Intrusion of the backbone. Its truncated apex pre- 
sents to the neck ; Its concave base IB formed by the 
diaphragm. The cavity is divided into a pah* of large 
pleural cavities, right and left, for the lungs, and a third 
submedlan pericardia! cavity for the heart. Where the 
opposite pleural cavities do not quite meet and fit, both 
before and behind, ts an interplenral Bpace, the anterior 
and posterior mediaatinal cavity, or premediastinum and 
poet mediastinum. Besides tne heart and lungs and 
their respective serous sacs (pericardium and pleura), the 
thorax contains many other structures, as the thoracic 
duct and thoracic aorta, many branches of the latter, etc. 
The thorax of other mammals differs from that of man 
chiefly in size, shape, degree of movability, etc., but not in 
actual structure or office, (b) In birds the thorax is rela- 
tively very capacious and expansive. The sternum is of 
enormous size ; long ribs frequently extend Into the sacral 
region, and others, shorter, Into the cervical region, so that 
the thorax encroaches In both directions. Its cavity is not 
shut off from that of the abdomen by any diaphragm. The 
ribs have a movable Joint between their vertebral and ster- 
nal parts, contributing to the expansibility of the chest. 
Most of the abdominal as well art proper thoracic viscera are 
actually inclosed by the thoracic walls. See cut under epi- 
plettra. (c) In those reptiles and batrachians which have 
breast-bones a thorax is distinguished much as it is in 
higher vertebrates. In serpents, which have no sternum, 
and whose ribs extend from head to tail, there is no distinc- 
tion between thorax and abdomen ; and the case is similar 
with turtles. In a few reptiles the thorax develops wing- 
like parachutes serving fora kind of flight, (d) In fishes 
a thorax, or a thoracabdominal region, is usually well 
marked by long ribs from a post anal solid and fleshy put 
of the body, but there IB no distinction of thoracic and ab- 
dominal cavities. The thorax may bear the pectoral fins, 
or these and the ventrals, or neither. 
2. In enfant., that part of the body which is 
situated between the head and the abdomen, 
and in adult insects alone bears the wings and 
leffS, when there are any. in the typical or hexapod 
insects the thorax is almost always a well-marked region, 
distinguished from the head in front and from the abdo- 
men behind by bearing the only locomotory appendages 
which these Insects possess iu the adult state namely, 
one or two pairs of wings and three pairs of legs. The thorax 
typically consists of three segments or somites of the 
IKM.V, one to each pair of legs, respectively named, from 
before backward, tne pnrfttnrax, the mftothorax, and the 
tnrtathorax, or sometimes the pry/Aorwjr, mfdithorax. and 
