The Trachea begins at the level of the cricoid cartilage (C6) and ends below the sternal angle (T4-T5). The site of division into right and left primary bronchi, which are of unequal size, is marked internally by a sagittally placed ridge, the carina. The trachea is rounded off anteriorly and laterally, flattened behind and has a transverse diameter of 1.3-2.2 cm.