trachea

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Anatomy A thin-walled, cartilaginous tube descending from the larynx to the bronchi and carrying air to the lungs. Also called windpipe.
2. n. Zoology One of the internal respiratory tubes of insects and some other terrestrial arthropods.
3. n. Botany One of the tubular conductive vessels in the xylem of vascular plants.

Century Dictionary and Cyclopedia

1. n. In anatomy and zoäl.: The principal air-passage of the body; the windpipe, beginning at the larynx and ending at the bronchial tubes. In Arthropoda, as insects, one of the tubes which traverse the body and generally open by stigmata upon the exterior, thus bringing air to the blood and tissues generally, and constituting special respiratory organs. It is a musculomembranous tube, stiffened and held open by a series of many cartilaginous or osseous rings, the first of which is usually specialized (see cricoid), and the last one or more of which are variously modified to provide for the forking of the single tracheal tube into a pair of right and left bronchial tubes (see pessulus). Through the larynx the trachea communicates with the mouth and nose and so with the exterior, and through the bronchial tubes with the lungs; and air passes through it at each inspiration and expiration. The trachea exists in all vertebrates which breathe air with lungs, and is subject to comparatively little variation in character. In man the trachea is a cylindrical membranocartilaginous tube about as thick as one's finger, and 4½ inches long, extending from the sixth cervical to the fourth dorsal vertebra, where it branches into the bronchi, lying along the front of the spinal column, the esophagus interposing between it and the vertebræ. The thyroid body is saddled upon it. Its structure includes many cartilaginous rings, some white fibrous tissue, yellow elastic tissue, muscular fibers, mucous membrane, and glands, besides nerves and blood-vessels. The tracheal rings (see ring) are from sixteen to twenty in number, incomplete in a part of their circumference, being about one third filled in by fibrous tissue. The highly modified first ring, or cricoid, is usually excluded from this association and described as a part of the larynx. Tracheal mucous glands are found in abundance as small flattened oval bodies, with excretory ducts which pierce the fibrous, muscular, and mucous coats to open on the surface of the mucous membrane. The arteries of the trachea are derived from the inferior thyroid; the tracheal veins empty in the thyroid vein; the nerves are from the pneumogastric and recurrent and the sympathetic. The trachea in other mammals resembles that of man. In birds the trachea presents several peculiarities; especially in long-necked birds this organ does not always follow the S-shaped curve of the cervical vertebraæ, and requires special contrivance for shortening and lengthening when the neck is bent and straightened. The whole structure is highly elastic, and the rings are peculiarly beveled on opposite sides alternately, so that each one may slip half over another to right and left. In some long-necked birds, as cranes and swans, the windpipe makes large folds or coils in the interior of the breast-bone or under the skin of the breast. The rings are prone to ossify in birds, and some of them are often greatly enlarged in caliber and soldered together into a large gristly or bony capsule, the tracheal tympanum, also called labyrinth. Besides its intrinsic muscles, the trachea is provided with others which pass to the furculum or sternum, or both. The lower end of the trachea is peculiarly modified in nearly all birds to form the lower larynx, or syrinx. See syrinx, 4 (with cut), also cuts under larynx, lung, pessulus.
2. n. In botany, a duct or vessel; a row or chain of cells that have lost their intervening partitions and have become a single long canal or vessel. They may be covered with various kinds of markings or thickenings, of which the spiral may be taken as the type. See vessel.
3. n. A notable genus of noctuid moths, containing one species, T. piniperda, known to English collectors as the pinebeauty. It is a common pest to pine and fir forests in Scotland and through northern and central Europe. The larva is slender, naked, and green, with three white lines on the back and a yellow or red line on the sides, and feeds on the older pine-needles. It passes the winter as pupa on or under the ground. This genus was named by Hübner in 1816.

Wiktionary

1. n. anatomy A thin-walled, cartilaginous tube connecting the larynx to the bronchi; the windpipe.
2. n. botany, dated xylem vessel
3. n. entomology the respiratory system of insects

GNU Webster's 1913

1. n. (Anat.) The windpipe. See Illust. of Lung.
2. n. (Zoöl.) One of the respiratory tubes of insects and arachnids.
3. n. (Bot.) One of the large cells in woody tissue which have spiral, annular, or other markings, and are connected longitudinally so as to form continuous ducts.

WordNet 3.0

1. n. membranous tube with cartilaginous rings that conveys inhaled air from the larynx to the bronchi
2. n. one of the tubules forming the respiratory system of most insects and many arachnids