Here's the epithelial lining, at higher magnification. The esophageal lumen is at upper right in this image.
The epithelium here is stratified squamous epithelium. In domestic animals the lining of the esophagus is keratinized, sometimes quite heavily.
Stratified squamous epithelium is well suited to this particular location. The level of abrasion is high and the proliferative nature of stratified squamous epithelium can be used to replace that which is worn away. Although this is a "wet" situation, the epithelium of the esophageal mucosa often has a stratum granulosum.
Monkey esophagus; H&E stain, 1.5 µm plastic section, 100x
