7 



until finally the cavity of the umbilical cord contains only the 

 elongated vitelline vessels (Fig. 5). 



Macroscopically these vessels present the appearance of 

 fine threads. They can be identified in an embryo of fifteen 

 millimetres, or more easily in an older one, and curiously 

 enough I find that the artery is pervious at birth and can be 

 injected with Teischmann's mass. 



It is my belief that the fixation of the ileum is more 

 directly due to the artery than to the vein. In all my sec- 

 tions the artery lies within the mesentery of the intestine, 

 whereas the vein does not seem to be actually connected 

 with it, but is placed close to it. A glance at Fig. 8 will 

 make this quite clear. It is a frontal section through the 

 cavity of the umbilical cord of an embryo of 13^ millimetres. 

 The vitelline artery may be recognized in the tissue of the 

 mesentery which is connecting together two bits of intestine. 

 The vein lies cephalad from it, quite isolated and alone. For 

 this reason it seems probable that the artery is a more potent 

 factor in the fixation of the ileum than the vein. 



Mall finds that in the human embryo the caecum is the 

 last portion of the intestine to enter the abdominal cavity. 



It seems to me more than probable that the order of 

 entrance in the human subject will also be found to depend 

 upon the vitelline artery, as I find that in the few human 

 embryos at my disposal the relation of the vessels to the in- 

 testine, as well as a persistence of them after the intestines 

 are intra-abdominal, resembles very closely their relation in 

 the cat. 



The abdominal cavities of ninety-three cats were examined 

 for Meckel's diverticulum, but in vain. This can probably 

 be accounted for by the very early separation of the yolk 

 sack from the intestine. Its absence was a disappointment 

 to me, for if it could have been found in a sufficient number 

 of cases to establish its normal position, it would have been 

 interesting to compare it with the position of the human di- 

 verticulum. Since the caecum enters the abdomen first in the 

 cat and last in the human subject, one would expect to find 

 the diverticulum farther from the caecum in the former than 



