Bronchi

Bronchi are the subdivisions of the trachea or windpipe. Opposite the third dorsal vertebra, the windpipe divides into two branches or bronchi, of similar structure to itself—namely, round and cartilaginous in front; and flat, with muscular and fibrous tissue behind, lined with mucous membrane. Of these bronchi, one goes to each lung, the right being little more than an inch; the left, about two inches in length. On entering the substance of the lung, the bronchi divide into smaller branches, which again subdivide, until they are no larger in diameter than $\backslash frac\{1\}\{50\}$th to $\backslash frac\{1\}\{100\}$th of an inch, and give origin to, or terminate in, small polyhedral sacs, which seem to cluster round their extremities, and open into them. These are the air-cells; they consist of elastic tissue, with a lining of mucous membrane, and beneath the latter, a layer of minute blood-vessels of the lung. See LUNGS, RESPIRATION.