Constrictions of the esophagus, when measured from upper incisors, are present at?

It is a fibromuscular tube, about 25 cm long in an adult. It extends from the lower end of the pharynx (C6) to the cardiac end of the stomach (Til). It runs Vertically but inclines to the left from its origin to thoracic inlet and again from T7 to oesophageal opening in the diaphragm. It shows three normal constrictions and it is important to know their location at oesophagoscopy. They are: At the pharyngo-oesophageal junction (C6) - 15 cm from the upper incisors. At the crossing of the arch of the aorta and left main bronchus (T 4) - 25 cm from upper incisors. Where it pierces the diaphragm (T 10) - 40 cm from upper incisors. (Foreign bodies in the oesophagus can be held up at these constrictions)