Scanning electron microscopic study of intestinal mucosa of the Nile crocodile (Crocodylus niloticus)

As part of an ongoing study of the intestinal tract of the Nile crocodile Crocodylus niloticus, the appearance of the small intestinal mucosa was examined using a scanning electron microscope (SEM). The duodenum displayed ridge-like and complex primary folds, both of which were arranged in a longitudinally directed zigzag pattern. The two types of folds alternated with each other, with the second type following the zigzag contours of the first. The folds were covered with polygonal- and dome-shaped epithelial cells. The latter cell type was less common and was restricted in location to the proximal two thirds of the mucosal folds. Both types of epithelial cells were covered with stubby microvilli which displayed a distinct linear arrangement. Goblet cells were present between the absorptive cells. In the jejunum the basic pattern of the folds persisted except that both types of primary folds became tall and leaf-like. The angle of the zigzag pattern was less acute than in the duodenum. In the ileum the two types of alternating folds decreased in height and were arranged in a longitudinally directed wave-like fashion. The zigzag mucosal folds of the small intestine ended abruptly at the ileorectal junction. The rectum displayed low, irregular folds which formed occasional large, puckered, rosette-shaped structures. The particular arrangement of the intestinal folds fulfills the dual function of promoting the absorptive process and facilitating the smooth passage of the intestinal contents. © 1995 Wiley-Liss, Inc.