INTESTINAL NUTRITION IN THE OPOSSUM 347 



the folds are filled with vessels which are of great size. This 

 condition does not appear in the drawing of the model, but can 

 be seen in segments of it and in sections of the embryo (fig. 1). 

 In one crypt the mucosa is spread out in a thin layer over a 

 large blood sinus. 



In addition to this great vascularity of the small intestine of 

 the earlier opossum embryos, there are certain other features of 

 interest in the morphology of the intestinal tract not only in 

 the late embryo, but in the pouch-young. 



In the late embryo: The duodenum extends from the pylorus 

 to the right side of the abdominal cavity, bends dorsally in a 

 right angle and proceeds downward and backward to the mid- 

 sagittal region, where it turns sharply back on itself and parallels 

 its course to the pylorus. The duodenum may arbitrarily be 

 said to end at this point. Here, at the upper end of limb 4 in 

 figures 3 and 7, the small intestine makes another complete bend 

 and follows the previous limb, lying mesially to it, for half its 

 length, then turns in a right angle to the left side of the body 

 (fig. 3, 5 to 6) and gradually bends upward to the region beneath 

 the corpus of the stomach. Here for a third time it turns sharply 

 back on itself as far as the midventral plane, where three short 

 loops (fig. 3, 8 to 12) are made before it leads into the large 

 intestine. The small coils are surrounded and partially covered 

 by the larger loops. The position of the union of the small 

 with the large intestine is on the left side of the body just below 

 the middle part of the stomach (behind 12 m. fig. 3). 



The first double loop of the small intestine — duodenum — has 

 a very wide diameter, being enlarged into an antrum pressing 

 against and encroaching upon the stomach. The widest region 

 of the whole intestinal tract is at the middle of the first limb of 

 this loop; the enlargement is a short distance below the opening 

 of the ductus choledochus. Beyond the duodenum the small 

 intestine — from the beginning of limb 5 in figure 3 — gradually 

 diminishes in caliber so that the girth of the smallest coils in the 

 umbilical region is about one-third that of the duodenum in its 

 widest place. The small intestine consists of relatively a few 

 loops, which in most cases have sharp bends. Segments of most 



