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The microscopic anatomy of the digestive tract of sus scrofa domestica MacLean, D. W.


A microscopic study of the complete digestive tract with its' appendages, was made on the pig. A marked resemblamce was noted between the digestive tract of the pig, and that of the human, A few outstanding differences were observed however. The wall of the digestive tract was composed of the following layers, a mucous membrane comprised of an inner epithelial lining; a tunica propria and a muscularis mucosa; a fairly thick submucosa; a lamina muscularis come prised of an inner circular layer and an outer longitudinal layer; and an outer adventitia or serosa, depending on the organs' location. The epithelium of the mouth is thick stratified squamous epithelium. The body of the tongue consists entirely of striated muscles. It is surrounded by a submucosa, and the whole Is covered with a thick stratified squamous epithelium. Very few papilla were observed on the tongue. All of the salivary glands were similarly constructed. The acini of the submaxillary and sublingual glands contained chiefly mucous-type cells, while the parotid acini were entirely serous in nature. A muscularis mucosa was found throuout the length of the oesophagus, although It was thinner in the upper than in the mid and lower portions. Numerous mucous-type glands were found in the submucosa of the oesophagus, but cardiac or superficial glands could not be demonstrated. The stratified squamous epithelium of the oesophagus was continued for a short distance into the oesophageal portion of the stomach, but changed rather abruptly to simple columnar epithelium at the junction of the oesophageal and fundic portions of the stomach, and continued as such as far as the anus. There were found to be three distinct glandular regions in the stomach, and a small non-glandular portion. The small intestine was characterized by villi and plica circulares. Brunners glands were observed in the duodenum, and an extremely large number of Peyers’ patches were observed in the ileum8 Goblet cells were observed in the epithelial lining of both the large and small intestine, and were most numerous in the colon and rectum. The large intestine is characterized by having no villi. The muscularis mucosa is much thicker in the large intestine than in the small intestine. The liver and pancreas were both similar in structure to those of mammals. It is worthwhile noting however, that in the liver of the very young pig the lobules are not completely separated by connective tissue septa, while in the liver of an older pig the lobules are completely separated by fairly thick connective tissue septa.

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