Carina

The carina is a cartilaginous ridge within the trachea that runs antero-posteriorly between the two primary bronchi at the site of the tracheal bifurcation (at the lower end of the trachea usually at the level of the 5th thoracic vertebra, which is in line with the angle of Louis, but may raise or descend up to two vertebrae higher or lower with breathing). 

This carina lies to the left of the midline. Inhaled foreign bodies are more likely to enter the right main bronchus.

The mucous membrane of the carina is the most sensitive area of the trachea and larynx for triggering a cough reflex. Widening and distortion of the carina is a serious sign because it usually indicates carcinoma of the lymph nodes around the region where the trachea divides.