OMPHALO-MESENTERIC ARTERIES IN THE MANATEE. 275 



forming one arteria omphalo-mesenterica, the future superior 

 mesenteric arteiy, and in the part where, ventrally to tlie ileum, 

 they run towards the umbilicus; Broman calls this hist part — 

 which runs outside of the gut together with the vitelline duct, 

 towards the umbilicus and in the umbilical cord— the vitelline 

 ;-\rtery. 



In some animals the arterise omphalo-mesentericJB, though not 

 paired in their proximal and distal parts, remain for some time 

 paired in the part which runs on both sides of the ileum, thus 

 forming a ring around the ileum, which, starting dorsally from 

 the single arteria omphalo-mesenterica., passes on the ventral 

 •side of the ileum into the single arteria vitellina, which runs 

 toward the um])ilicns iu the mesodermic vitelline stalk. 



In most animals this part does not remain paired, the artery 

 on one side disappearing (the left in some animals, in others 

 the i-ight), the persisting arcery of the other side I'unning on the 

 lateral surface of the ileum, but deviating from its wall, so as to 

 produce a peritoneal fold ; usually this fold later on loses its 

 connection with the wall of the ileum and thus, as the beginning 

 of the arteria vitellina, passes on the mesoileum. 



When after the disappearance of the vitelline duct, the vitelline 

 jirtery also disappears, the mesodermal yolk -sac -stalk grows 

 thinner and thinner, ruptures, and finally vanishes. 



Broman in the paper I have cited proves that during this 

 process we meet with variable conditions in different animals. 

 Thus, in some animals until birth the vasa omphalo-mesenterica 

 can remain visible always, in others abnormally ; but usually 

 they disappear in the foetus, and leave behind them folds, 

 i-unning towards the innbilicus, which persist in some animals 

 only for a short period of their foetal life, in others until birth 

 and sometimes even in extra-uterine life in the adult animal. 

 These folds, running towards the umbilicus, rupture, and either 

 vanish completel}'' or (either only in iVetus or new-born or adidt 

 animals) form bands adherent to the dorsal mesentery, brt 

 hanging freely down into the abdominal cavity. 



The remains of the vitelline vein which run towards the 

 mesoduodenum, Broman calls "appendix mesoduodeni," the 

 remains of the vitelline artery "appendix mesilei"; any |)art of 

 the ruptured yolk-duct-stalk remaining near the umbilicus, 

 " appendix umhilicalis." 



Broman noticed in an adult Castor fiber in the place where in 

 other new-born animals, or their foetuses, could be seen the 

 appendix mesilei, a remarkable fold, running from one side of 

 the mesileum to the wall of the ileum ; he explains it as the 

 remains of the fold, formed by the artery joining tlie ompha.lo- 

 mesentet'ic artery in the mesileum and the arteria vitellina in the 

 yolk-sac-stalk by separating from the wall of the ileum. • 



I see in this case of Castor fiber a complete analogy with the 

 condition in the Manatee, except that in the Manatee, in the place 

 ■of the appendix mesilei of other animals, such a fold appears on 



