The walls may be thrown into so many folds and cut so tangentially, that relationships are not immediately clear.  However, if you will find the esophageal end and follow along the length of its luminal surface, you will find at some point a very sharp transition from stratified squamous to a simple columnar epithelium.  Other coats of the wall have more of a zone of overlap and transition.

If your section has a thick wall, it is from a dog; if thin, from a cat.  Compare slides with a neighbor.  Although the epithelial transition is the same in both animals, the appearance of other coats varies.  Look for submucosal glands in the esophagus and mucosal (cardiac) glands in the stomach; notice their positional relationship to the muscularis mucosae in each instance.  In the muscularis externa is the muscle wholly smooth, or is it something skeletal? (Animals vary in this respect.)