<prompt> The toughest layer of the esophagus is theMucosaSubmucosaMuscularisAdventitia  <response>: C i.e. Muscularis Muscularis externa is the toughest layer of esophagusQ; upper 13rd is composed of skeletal muscleQ, lower 13rd is composed of smooth muscleQ the middle third is made up of both types of muscle. 