Bronchi

Bronchi, The trachea or windpipe, on its termination at the level of the third dorsal vertebra; bifurcates, and the two tubes into which it divides are called bronchi, right and left respectively,. Each main bronchus is rather more than an inch in length, the right being placed more horizontally, and the left being somewhat narrower but a little longer than the right. At their termination these tubes in their turn subdivide, forming the smaller bronchi, until ultimately the smallest subdivisions called bronchioles communicate with the groups of air cells. The main bronchi are almost identical in structure with the trachea (q.v.); in the smaller divisions the cartilage is irregularly disposed, and the unstriped muscle fibres assume an increasing importance as a constituent of the lining wall of these smaller tubes. In the smallest bronchioles no cartilage is found. The mucous membrane of the bronchi is lined throughout with ciliated columnar epithelium.