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The comparative histology of the esophagus and stomach of birds of different food habits Lazareff, Anne Eileen

Abstract

A histological investigation was carried out on the esophagus and stomach of the following birds: kingfisher (Megacercyle alcyon caurina), California murre (Uria aalgae Californioa), screeoh owl (Otus asio kennicotti),Peale's faloon (Falco peregrinius pealei), and sparrow hawk (Falco sparverius sparverius). A number of stains was used to intensify the different structures present. In the kingfisher, murre and owl the esophagus was a thin walled highly expansible tube of generally even calibre, whereas in the Peak's falcon the anterior part was dilated into a sac. The wall of the esophagus possessed the usual structure characteristic of this region of the digestive tube. Three types of glands have been distinguished in these birds. In the kingfisher and owl simple oval glands were situated almost entirely within the epithelium. The glands and excretory duct were composed of similar cells with slight variations occuring in excretory duct lengths. In the California murre the glands were still simple but had sunken to the tunica propria with just the excretory ducts passing through the epithelium. The gland cells were narrower, and the duct cells resembled those observed in the owl and the kingfisher. These glands were all apocrine secretory. However, in the Peale’s falcon and sparrow hawk secretion was holocrine. These glands were deeply embedded within the tunica propria and resembled the esophageal glands of the chicken. The excretory ducts were lined by squamous epithial cells. Although the birds examined possessed a variety of food habits: fish, mammals, birds and crustaceans, the food was essentially meat. However, considerable variations in the structure of the esophagus were observed. The proventriculus was comprised of: a mucosa, indented with minute gastric pits, a muscularis externa of three layers of smooth muscle, and a lamina adventitia that surrounded the entire tube. Within the mucosa the deep glands were situated. These were composed of large lobes, enveloped in a dense capsule of connective tissue and internally consisted of simple tubules that radiated about a central excretory duct. The structure of the proventriculus was more or less uniform in the birds investigated, with only slight variations occuring in cellular arrangement and cellular size. The gizzards in the birds examined were large spherical structures that filled a majority of the abdominal cavity. In the kingfisher, owl, Peale's falcon, and sparrow hawk, the gizzard was lined by a thin keratinoid lining that was secreted by the glands present in the gizzard mucosa. The muscularis externa was of approximately equal thickness throughout. In the murre, the keratinoid layer was five or six times as thick as in the above birds and the muscles showed a heavy development on the dorsal and ventral sides. This development took place toward a grinding mechanism that was necessary for processing the hard shelled crustaceans eaten by this bird.

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