In anatomy, the carina is a ridge of cartilage in the trachea that occurs between the division of the two main bronchi. This occurs at the lower end of the trachea (usually at the level of the 4th thoracic vertebra, which is in line with the sternal angle, but may raise or descend up to two vertebrae higher or lower with breathing). This ridge lies to the left of the midline, and runs antero-posteriorly (front to back). Foreign bodies that fall down the trachea are more likely to enter the right bronchus.
https://en.wikipedia.org/wiki/Carina_of_trachea
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9 patients were the carina and the bronchial spurs normally sharp and the mucous membrane normal in color at every examination.
https://jamanetwork.com/journals/jamapediatrics/article-abst...