The wall of the esophagus is stratified into a mucosal layer, submucosal layer, muscular layer, and tunica. The esophagus is a flat, round, muscular tube that transports food and is located anterior to the spine. The wall of the esophagus is divided into four layers, which are the mucosa, submucosa, muscularis propria, and tunica albuginea from the inside out. 1. Mucosal layer: The mucosal layer of the esophagus is moist and smooth, pink in color, and the mucosa of the lower esophagus is slightly light gray. There are 7-10 longitudinal folds on the mucosa, which are convex to the inner lumen and help the downflow of fluid. 2. Submucosa: The submucosa of the esophagus is composed of loose connective tissue, which lies between the mucosa and the muscularis propria. It contains large blood vessels, nerves, lymphatic vessels and esophageal glands. 3. Muscularis propria: the muscularis propria consists of two types of muscle fibers, the inner circular and outer longitudinal. The muscularis propria is mainly composed of transverse muscle in the upper 1/3 of the esophagus, a mixture of transverse and smooth muscle in the middle 1/3, and mainly smooth muscle in the lower 1/3. 4. Epithelium: the outer membrane of the esophagus, composed of loose connective tissue, contains nerves and vascular structures.