Digestive Tract of La Plata Dolphin, Pontoporia Blainvillei I. Oesophagus and Stomach

Abstract

The oesophagus and the stomach of more than half of the collected ninety-five Pontoporia blainvillei (body length 84.5-171 cm) were examined macroscopically and nine fresh specimens were observed light-microscopically. The oesophagus is an ordinary muscular tube which is lined with a thick stratified squamous epithelium and continues to the stomach with a distinct epithelial transition. The stomach of Pontoporia consists of three compartments; the first one is the glandular main stomach, the second is the connecting channel and the third is the pyloric stomach. The oesophageal forestomach, which is found in other dolphins, is not seen in Pontoporia. The main stomach is continuous from the oesophagus and is a pear-shaped firm sac. A narrow zone of cardiac glands was seen adjacent to the oesophagus and the rest of the glands consist of chief and parietal cells and possibly mucous neck cells. The ratio of the parietal cells to the chief cells is about 1: 3 or less. An opening which leads to the connecting channel can be seen near the bottom of the main stomach The connecting channel is situated slightly ventrally between the main and the pyloric stomachs. The channel initially directs downwards and then upwards with a sharp crooking. Its mucosa consists of mucous-like tubular glands. The pyloric stomach is a 3-shaped tubular compartment and is continuous from the connecting channel with an opening near its top, then leads to the duodenal ampulla with a small opening which contains circular smooth muscles. The glandular structure of the pyloric stomach is similar to that of the connecting channel. The structure of the stomach of Pontoporia was compared with that of other cetaceans, and the absence of the oesophageal forestomach in Pontoporia was especially discussed from the viewpoint of the function of the stomach, the living environment and the food habits of the animals. © 1974, Editorial Board of Okajimas Folia Anatomica Japonica. All rights reserved.