<prompt> The esophagus -Begins at the upper border of cricoid cartilageRuns a straight course throughoutIs narrowest at its terminationIs narrowest at its beginning  <response>: At the lower end of pharynx, at the level of lower border of cricoid cartilage, esophagus begins. It is narrowest at its beginning due to cricopharyngeal sphincter. Then it runs a curved route rather than being straight. 