18.96.] 



INTESTINAL TBACT OH BIEDS. 



137 



iipon Chauna '. I am thus able to display more clearly the relations 

 of the individual cases to each other and to what I talte 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 con- 

 dition 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- 



Rg. 1. 



Alligator mississipiensis ; intestinal tract, shovring a simple condition. 



" On the Anatomy of Chauna chavaria," P. Z. S. 1895, pp. 350-358, 



