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Show 1896.] INTESTINAL T R A C T O E BIRDS. 137 upon Chauna \ I am thus able to display more clearly the relations of the individual cases to each other and to what I take to be the primitive type, and to show the mesentery and the intestinal veins. The intestinal tract was removed from the body-cavity after section of the oesophagus and of the rectum above the cloaca. The stomach was placed to the right with its ventral side uppermost, and the loops of the intestine were folded outward. The condition of the material made it impossible to inject the vessels in enough cases to serve for comparison; but copious washing and the passage of a jet of water through the canal oxygenated the clotted blood in the veins and made it possible to trace their course. Where I was able to trace them, I found that the arteries followed the veins closely ; but it is only the veins that I describe here. In the simplest possible condition the intestine would run a straight course from the stomach to the cloaca, suspended to the dorsal wall of the body-cavity by a fold of mesentery. The intestine grows longer than the length of the body-cavity, and, in consequence, is thrown into a series of folds. The first of these, usually a single distinct loop, contains the pancreas; then follows a more irregularly folded portion, the mesentery of which is an arc of a circle, with its diameter attached to the dorsal body-wall, and the median point of its circumference stretching toward the ventral body-wall in the region where the yolk-sac was attached. The rectum is a portion of the gut which usually retains the primitive straight condition. In fig. 1, which I drew from a dis- Fig. 1. Alligator mississipiensis; intestinal tract, showing a simple condition. » " On the Anatomy of Chauna chavaria;' P. Z. S. 1895, pp. 350-358. |