THE UMBILICAL VESICLE. 



597 



After the young animal leaves the egg, the umbilical vesicle 

 in some species becomes withered and atrophied by the absorption 

 of its contents; while in others, the abdominal walls gradually 



Fig. 205. 



Young FISH with umbilical vesicle. 



extend over it, and crowd it back into the abdomen ; the nutritious 

 matter which it contained passing from the cavity of the vesicle 

 into that of the intestine by the narrow passage or canal which 

 remains open between them. 



In the human subject, however, as well as in the quadrupeds, the 

 umbilical vesicle becomes more completely separated from the abdo- 

 men than in the cases just mentioned. There is at first a wide com- 

 munication between the cavity of the umbilical vesicle and that of 

 the intestine ; and this communication, as in other instances, becomes 

 gradually narrowed by the increasing constriction of the abdominal 

 walls. Here, however, the constriction proceeds so far that the 

 opposite surfaces of the canal come in contact with each other, and 

 adhere ; so that the narrow passage previously 

 existing, between the cavity of the intestine 

 and that of the umbilical vesicle, is obliterated, 

 and the vesicle is then connected with the 

 abdomen only by an impervious cord. This 

 cord afterward elongates, and becomes con- 

 verted into a slender, thread-like pedicle (Fig. 

 206), passing out from the abdomen of the 

 foetus, and connected by its farther extremity 

 with the umbilical vesicle, which is filled with 

 a transparent, colorless fluid. The umbilical 

 vesicle is very distinctly visible in the human 

 foetus so late as the end of the third month. 

 After that period it diminishes in size, and is gradually lost in the 

 advancing development of the neighboring parts. 



In the formation of the umbilical vesicle, we have the first varia- 



Fig. 206. 



HCMAX EMBRYO, with 

 nmtiilical vesicle ; about the 

 fifth week. 



