The normal narrowing in the middle of the oesophagus is caused by
Azygos vein
Hemiazygos vein
Right main stem bronchus
Left main stem bronchus
Middle constriction of oesophagus is due to left bronchus .27.5cm/11 inch from insisor teeth. BD CHAURASIA&;S HUMAN ANATOMY VOLUME 1, 6TH Edition . page no 282, fig 20.7
Thorax