Anatomy of the Esophagus. The esophagus is a muscular tube about ten inches (25 cm.) long, extending from the hypopharynx to the stomach.The esophagus lies posterior to the trachea and the heart and passes through the mediastinum and the hiatus, an opening in the diaphragm, in its descent from the thoracic to the abdominal cavity.The esophagus has no serosal layer; tissue around the esophagus is called adventitia.he esophagus lies posterior to the trachea and the heart and passes through the mediastinum and the hiatus, an opening in the diaphragm, in its descent from the thoracic to the abdominal cavity. The esophagus has no serosal layer; tissue around the esophagus is called adventitia.