II.Three constrictions beginning,lies at level of C6,the narrowest part crossed by left main bronchus, 25cm from incisors,lies at level of intervertebral disc between T4 and T5. passes through the esophageal hiatus of diaphragm,40cm from incisors,at level of T10 Carcinoma of esophagusⅡ. Three constrictions  beginning, lies at level of C6, the narrowest part  crossed by left main bronchus, 25cm from incisors, lies at level of intervertebral disc between T4 and T5.  passes through the esophageal hiatus of diaphragm, 40cm from incisors, at level of T10 Carcinoma of esophagus