The mucous coat (tunica mucosa) is thick, of a reddish color above, and pale below. It is disposed in longitudinal folds, which disappear on distension of the tube. Its surface is studded with minute papillæ, and it is covered throughout with a thick layer of stratified squamous epithelium. Beneath the mucous membrane, between it and the areolar coat, is a layer of longitudinally arranged non-striped muscular fibers. This is the muscularis mucosæ. At the commencement of the esophagus it is absent, or only represented by a few scattered bundles; lower down it forms a considerable stratum.