A comparative histological study on the distribution of striated and smooth muscles and glands in the esophagus of wild birds and mammals.

Musculature and glands of the esophagus in various wild birds and mammals were examined histologically. Cervical and thoracic esophagi of all birds used (mallard, spot-billed duck, Ural owl and Hodgson's hawk-eagle) were comprised of smooth muscle fibers only. In contrast, esophagi of the nutria, Japanese raccoon dog, common raccoon and Japanese marten consisted largely of striated muscle fibers. In the masked palm civet, Japanese macaque and bottlenose dolphin, esophageal muscle layers consisted of both striated and smooth muscle fibers. Esophageal glands were observed except for the nutria and masked palm civet. These results show a wide variety of the structural composition in the esophagus of wild animals, particularly mammals, examined in this study.