الفهرس 
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Abstract
In the present study, 30 healthy mature pigeons as granivorous, cattle egrets as carnivorous, and ducks as omnivorous were used for the anatomical, histological, immunohistochemical, and ultrastructural studies. After euthaniziation the topographic anatomy of the esophagus and crops was detected. The mean length of the esophagus (cervical and thoracic regions) was measured. Esophagus and crops of the above-mentioned species were carefully dissected. The internal surfaces of the esophagus and crops were examined for the detection of the esophageal and crop inner folds.
The specimens for the light microscope were immediately fixed in 10% neutral buffered formalin (N.B.F.) after that, they were processed by paraffin technique. Sections of 5μm thickness were obtained. The obtained sections were stained with H&E, Crossman’s trichrome stain, Orcein stain, AB (pH 2.5), and PAS technique. For transmission electron microscopy, the specimens were fixed in buffered GA/FA fixative. Then processed till ultra-thin sections were obtained and stained with uranyl aetate and lead citrate.
Anatomically, the esophagus was a destindable muscular tube that situated on the right side of the neck and dorsally to the trachea. It comprised of two anatomical regions; cervical and thoracic regions interrupted with the crop which was highly developed only in the pigeons as two large lateral sacs and small median, while in the cattle egrets, the crop was spindle shape extension of the thoracic esophagus but in the ducks, the crop was an extension of the cervical regions. The cattle egret’s esophagus either the cervical or the thoracic region was the longest. The internal surface of the esophagus and cops was demarcated by parallel longitudinal folds which were thin overcrowded in the cervical regions and thick widely separated in the thoracic one of the three studied avian species. While the crop folds were honeycombed shape in the pigeons, separated by a deep groove in the cattle egrets and spirally coiled in the ducks.