noun
definition
One of a group of fishes having the ventral fins placed beneath the thorax or beneath the pectoral fins.
adjective
definition
Of the thorax.
Examples of thoracic in a Sentence
The lungs are small and occupy only the dorsal portion of the thoracic cavity.
When first sucked up by the insect from an infected man it passes into its stomach, and thence makes its way into the thoracic muscles, and there for some time it grows.
Dorsal vertebrae frequently have a ventral outgrowth of the centrum; these hypapophyses may be simple vertical blades, I-shaped, or paired knobs; they serve for the attachment of the thoracic origin of the longus collianticus muscle, reaching their greatest development in Sphenisci and Colymbidae.
In many birds some of the thoracic vertebrae are more or less coOssified, in most pigeons for instance the 15th to 17th; in most Galli the last cervical and the next three or four thoracics are coalesced, &c. The pelvic vertebrae include of course the sacrum.
The most anterior part of the ilium often overlaps one or more short lumbar ribs and fuses with them, or even a long, complete thoracic rib.
In the region of the neck lateral strands pass through the transverse canal of the cervical vertebrae; but from the thoracic region onwards, where the cardiac branch to the heart is given off, each strand is double and the basal ganglia are successively connected with the next by a branch which runs ventrally over the capitulum of the rib, and by another which passes directly through the foramen or space formed between capitulum and tuberculum.
The ventral region of the thoracic skeleton is complex, each segment usually possessing a median sternum with paired episterna (in front) and epimera (behind).
The nervous system is remarkably concentrated in some beetles, the abdominal ganglia showing a tendency to become shifted forward and crowded together, and in certain chafers all the thoracic and abdominal ganglia are fused into a single nervecentre situated in the thorax, - a degree of specialization only matched in the insectan class among the Hemiptera and some muscid flies.
The head - carrying feelers, mandibles and two pairs of maxillae - is succeeded by the three thoracic segments, each bearing a pair of strong five-segmented legs, whose feet, like those of the adult, carry two claws.
For the appreciation of the sounds made by these stridulators, the ants are furnished with delicate organs of hearing (chordotonal organs) in the head, in the three thoracic and two of the abdominal segments and in the shins of the legs.
From these three pairs of thoracic legs comes the name - Hexapoda - which distinguishes the class.
The legs, wings and other organs of the trunk receive their nerves from the thoracic and abdominal ganglia, and the fusion of several pairs of these ganglia may be regarded as corresponding to a centralization of individuality.
From these facts it appears that the anterior three divisions of the head differ strongly from the posterior three, which greatly resemble thoracic segments; hence it has been thought possible that the anterior divisions may represent a primitive head, to which three segments and their leg-like appendages were subsequently added to form the head as it now exists.
Though the T hx, thoracic segments bear the wings, no trace of these appendages exists till the close of the embryonic life, 8 `' nor even, in many cases, till much later.
The thoracic segments, as seen in an early stage of the ventral plate, display in a well-marked manner the essential elements of the insect segment.
In the embryos of many insects there are projections from the segments of the abdomen similar, to a considerable extent, to the rudimentary thoracic legs.
The nervous system of the embryonic head exhibits three ganglionic masses, anterior to the thoracic ganglionic masses; these three masses subsequently amalgamate and form the sub-oesophageal ganglion, which supplies the trophal segments.
But the pupa hangs from the surface by means of paired respiratory trumpets on the prothorax, the dorsal thoracic surface, where the cuticle splits to allow the emergence of the fly, being thus directed towards the upper air.
Young resembling parents, but aquatic in habit, breathing dissolved air by thoracic tracheal gills.
Larvae eruciform without thoracic legs, or vermiform without head-capsule.
Insect wings are specialized outgrowths of certain thoracic segments, and are quite unrepresented in any other class of Arthropods.
The origin of insect wings remains, therefore, a mystery, deepened by the difficulty of imagining any probable use for thoracic outgrowths, comparable to the wingrudiments of the Exopterygota, in the early stages of their evolution.
As shown by the number and variety of species, the Orthoptera are the most dominant order of this group. Eminently terrestrial in habit, the differentiation of their fore-wings and hindwings can be traced from Carboniferous, isopteroid ancestors through intermediate Mesozoic forms. The Plecoptera resemble the Ephemeroptera and Odonata in the aquatic habits of their larvae, and by the occasional presence of tufted thoracic gills in the imago exhibit an aquatic character unknown in any other winged insects.
There are three distinct and large thoracic segments, whereof the prothorax is narrower than the others; the legs are much shorter and stouter than in the winged insect, with monomerous tarsi terminated by a single claw.
His results, so far, have been confirmed by Starling, who finds that the amount of lymph-flow from the thoracic duct is dependent upon difference in pressure.
In the treatment of effusions into the pleura and, though with less advantage, of pericardial effusions, direct mechanical interference was practised by one physician and another, till these means of attaining rapid and complete cure took their places as indispensable, and were extended from thoracic diseases to those of the abdominal and other inner parts formerly beyond the reach of direct therapeutics.
The discovery of the Rntgen rays has also extended the physician's power of vision, as in cases of aortic aneurysm, and other thoracic diseases.
H, Head; 1, 2, 3, the thoracic segments; i., ii., the first and second abdominal segments; i., being the propodeum.
But the most natural division is obtained by the separation of the saw-flies as a primitive sub-order, characterized by the imperfect union of the first abdominal segment with the thorax, and by the broad base of the abdomen, so that there is no median constriction or " waist," and by the presence of thoracic legs - usually also of abdominal pro-legs - in the larva.
The soft, white larvae have the thoracic legs very small and feed in the stems of various plants.
The Tenthredinidae, or true saw-flies, are distinguished by two spines on each fore-shin, while the larvae are usually caterpillars, with three pairs of thoracic legs, and from six to eight pairs of abdominal prolegs, the latter not possessing the hooks found on the pro-legs of lepidopterous caterpillars.
In the adult there is a pair of such glands opening ventrally on the hindmost thoracic segment, or at the base of the abdomen; but in the young insect the glands are situated dorsally and open to the exterior on a variable number of the abdominal terga.
The Notonectidae breathe mostly through the thoracic spiracles; the air is conveyed to these from the tail-end, which is brought to the surface, along a kind of tunnel formed by overlapping hairs.
The name of shrimps is sometimes given to members of the order Schizopoda, which differ from most of the Macrura in having swimming branches or exopodites on the thoracic legs.
It may be objected that hereby the term pleon is used in two different senses, first applying to the abdomen alone and then to the abdomen plus the last thoracic segment.
To the left of the vena cava is the Spigelian lobe, which lies in front of the bodies of the tenth and eleventh thoracic vertebrae, the lesser sac of peritoneum, diaphragm and thoracic aorta intervening.
The cyst should be treated like a liver-abscess, by incision through the abdominal or thoracic wall, by circumferential suturing and by exploration and drainage.
Some of the families - the stone-flies, for example - have the young insect much like the adult, growing its wings visibly outside the thoracic segments, and active at all stages of its life.
A remarkable point in the Plecoptera is the presence in some forms (Pteronarcys) of small branching gills on the three thoracic and the front abdominal segments.
There are generally nineteen dorso-lumbar vertebrae (thirteen thoracic and six lumbar), the form of which varies in different genera; in the cursorial and leaping species the lumbar transverse processes are generally very long, and in the hares there are large compressed inferior spines, or hypapophyses.
The second thoracic ring is humped, and there is a spine-like horn or protuberance at the tail.
The cervical and thoracic vertebrae seem to be biconcave; the cervical ribs are much reduced and were apparently still movable; the thoracic ribs are devoid of uncinate processes.
Thus, in the thoracic limbs of the Malacostraca, the endopodite generally forms a walking-leg while the exopodite becomes a swimmingbranch or may disappear altogether.
It is highly characteristic of the Malacostraca, however, that the trunk-limbs are divided into two sharply defined tagmata corresponding to the thoracic and abdominal regions respectively, the limit between the two being marked by the position of the male genital openings.
The thoracic limbs have the endopodites converted, as a rule, into more or less efficient walking-legs, and the exopodites are often lost, while the abdominal limbs more generally preserve the biramous form and are, in the more primitive types, natatory.
In the thoracic series it is usual for one or more of the anterior pairs to be pressed into the service of the mouth, forming " foot-jaws " or maxillipeds.
In the primitive Malacostraca the gills were probably, as in the Phyllopoda and in Nebalia, the modified epipodites of the thoracic limbs, and this is the condition found in some Schizopoda.
In the Amphipoda, the gills though arising from the inner side of the bases of the thoracic legs are probably also epipodial in nature.
The gills are inserted at the base of the thoracic limbs, and lie within a pair of branchial chambers covered by the carapace.
These may be formed by the modification of almost any of the appendages, often the antennules or antennae or some of the thoracic limbs, or even the mandibular palps (some Ostracoda).