ASPERA ARTERIA

ASPERA ARTERIA,in Anatomy, the Wind-pipe; otherwise called the Trachea. See TRACHEA and ARTERY. The Aspera Arteria, is a Canal situated in the Fore-part of the Neck, before the Oesophagus: Its upper End is called the Larynx; from whence it descends to the fourth Vertebra of the Back, where it divides and enters the Lungs. See OESOPHAGUS, LARYNX, VERTEBRA, etc. It is formed of annular Cartilages ranged at small and equal Distances from one another, growing smaller and smaller, as they approach the Lungs; and those of the Bronchia so close to one another, that, in Expiration, the second enters within the first, and the third within the second, and the following always enters the preceding.
See RESPIRATION, etc. Between the Larynx and the Lungs, these Cartilages make not complete Rings; but their hind Part, which is contiguous to the Oesophagus, is membranous, that they may better contract and dilate, and give way to the Food as it passes down the Gullet. See DEGLUTITION. The Cartilages of the Bronchia are completely annular, or their capillary Branches have no Cartilages, but instead of them small circular Ligaments, which are at pretty large Distances from one another.—The Use of the Cartilages, is to keep the Passage for the Air open; but in the capillary Bronchia, they would hinder the subsiding of the Vessels. See BRONCHIA. These Cartilages are tied together by two Membranes, external and internal: the external is composed of circular Fibres, and covers the whole Trachea externally; the internal is of an exquisite Sense, and covers the Cartilages internally: it is composed of three distinct Membranes; the first, woven of two Orders of Fibres; those of the first Order being longitudinal, for the shortening the Trachea; these make the Cartilages approach and enter one another: the other Order is of circular Fibres, for the contracting the Cartilages.



When these two Orders of Fibres act,they assist, together with the external Membrane, in Expiration, in Coughing, and in Altering the Tone of the Voice. See Expiration, Voice, etc. The second Membraneis altogether glandulous; and the excretory Vessels of its Glands opening into the Cavity of the Trachea, secrete a Liquor for moistening the same, and defending it from the effects of the Air.—The last is a Net of Veins, Nerves, and Arteries; the Veins are Branches of the Vena Cava, the Nerves of the Recurrent; and the Arteries, Sprigs of the Carotides. See further under the Article TRACHEA.

ASPERA ARTERIA