The trachea bifurcates into right and left mainstem bronchi at approximatley the level of T5; this is called the carina. The right mainstem bronchus is wider. shorter, and more vertical in orientation than the left. At the hilum the mainstem bronchi enter the lungs and divide into lobar bronchi, and they correspond to the lobes of the lungs; which means there are three on the right and two on the left.  There is further division into tertiary or segmental bronchi, they extend into the bronchopulmonary segments. Typically there are ten segments in each lung. Each lung functions independently and can be removed surgically.