In an AP view, the carina lies at a level between the attachments of the second and third ribs to the sternum. The right main stem bronchus continues caudally at an obtuse angle to the axis of the trachea, leading to increased probability of aspiration to the right. The right upper lobe bronchus takes off almost immediately after the carinal split. The bronchus intermedius continues between the right upper lobe bronchus, and the anterior take-off of the right middle lobe bronchus. The short right lower lobe bronchus splits into segments almost immediately. The left main stem bronchus takes off more sharply, and has a slight upward curve before dividing into upper and lower lobe bronchi. The left upper lobe bronchus divides into segments corresponding to the left upper lobe, and into the attached lingular branches.
The secondary and tertiary segmental bronchi are shown (see bronchopulmonary segments). Note the common secondary apical posterior and anteromedial basal bronchi on the left. also note the takeoff of the superior basal segmental bronchus on the right almost directly opposite the middle lobe bronchus, and the corresponding segment on the left arising from the beginning of the lower lobe bronchus.
Link to this frame from your Personal Thumbnails page?