Esophagus: The esophagus is a muscular tube about ten inches (25 cm) long extending from the hypopharynx to the stomach. The peristaltic motion of the esophagus moves food along 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. There are three segments or regions of the esophagus: cervical, thoracic and abdominal. The esophagus may also be described in terms of upper, mid, and lower thirds. These measurements are not the same thing. The inner wall of the esophagus is lined with mucosa. The mucosa can be subdivided into surface epithelium, lamina propria, and muscularis mucosae. Beneath the mucosa lies the submucosa. The muscularis propria lies beneath the submucosa. There is no serosa on the esophagus, but rather an external adventitia of fibrous connective tissue. The lack of a serosa facilitates the spread of cancer beyond the primary site into adjacent tissues and lymph nodes. Branches of the aorta and celiac artery supply blood to the esophagus. The venous drainage is to the azygos, thryoid, and left gastric veins. The lymphatic vessels drain into the cervical, mediastinal, and gastric lymph nodes depending on the segment of the esophagus from which they originate.