True about tracheal bifurcation -

Trachea The trachea is 10-15 cm long tube formed by C-Shaped hyaline cartilaginous rings and fibromuscular membrane. It extends from the lower border of cricoid cartilage (at C6 level) to lower border of T4 or upper border of T5 vertebra (T4-T5 disc space) where it bifurcates. Its external diameter is about 2 cm in males and about 1.5 cm in females. It has 16-20 cartilaginous rings. The first tracheal ring is the broadest. The last ring at tracheal bifurcation shows carina, a triangular hoop-shaped process separating the bronchi, i.e. Carina is a bifurcation of the trachea. The trachea is lined by ciliated columnar epithelium.  It is supplied by the inferior thyroid artery and is drained by left brachiocephalic vein.  Sensory and motor supply to the trachea is provided by the parasympathetic system through vagi and recurrent laryngeal nerve. Vasomotor supply is by sympathetic fibres through middle cervical ganglion along inferior thyroid arteries.