276 OMPHALO-MESENTEKIC ARTERIES IN THE MANATEE. 



both sides. This shows that in the Manatee the paired parts of 

 the vitelline arteries, which enclose on both sides the ileum, must 

 have persisted for a longer time than in other animals, and, 

 deviating symmetrically from the wall of the ileum, must have 

 formed symmetrical peritoneal folds. As in Castor fiber the 

 one-sided fold, so here the paired folds persisted in the adult 

 animal. 



The fact, that those paired folds meet on the ventral wall of 

 the ileum, forming a sort of bridge, appears quite natural, 

 considering that the omphalo-mesenteric arteries joined on the 

 ventral wall of the ileum and from there ran toward the 

 umbilicus in the yolk-sac-stalk, which in the foetus which I 

 examined was still preserved. 



