Pyloric stomach of S. fuscus: (A) pyloric folds in the stomach mucosa; (B) pyloric mucosa, primary fold (a) with evaginations of the lamina propria, with nonglandular secondary folds (b); (C) pyloric with muscles (c) serosa (d) with conjunctive of pyloric ...
The muscle layer of the stomach has an inner layer of smooth muscle fibers set in a circular arrangement and an outer layer of longitudinally placed fibers. The cardiac region of the stomach contains scattered skeletal striated fibers that may have originated in the esophageal region (Figures 4(A) and 4(C)). The most developed muscle layer is found in the pyloric region. The serosa along the whole stomach is a thin dense connective tissue limited by a single layer of flat mesothelial cells. In the pyloric stomach, the serous membrane is continuous with the connective tissue of the serous sac that houses the pyloric caeca (Figure 6(C)).
3.2.2. Pyloric Caeca
Three long caeca are present after the pyloric sphincter at the junction of the stomach with the intestine (Figure 7(A)). The mucosa with long folds (Figure 7(B)) is comprised of a single-layered epithelium with cylindrical cells (Figure 7(C)) and lamina propria of loose connective tissue containing small vessels without glands (Figure 7(D)). An epithelium containing prismatic cells (absorptive cells responsible for nutritional absorption) was observed. In the spaces, mucous-producing goblet cells were found, which lubricate the caecal and the intestinal wall (Figures 7(A) and 7(D)). There is no submucosa, instead a thin circular layer of smooth muscle is present.