The Fetal Circidatioyi 331 



Prior to birth, the vitelline vessels have disappeared except in 

 so far as the}^ have persisted as portions of other vessels within 

 the body. As soon as birth takes place and the umbilical cord 

 is ruptured or the placenta detached from the uterus, the allantoic 

 circulation must abruptly cease, while the pulmonary circulation 

 must be promptly established because the respiratory functions 

 have been shifted from the placenta to the lungs. 



As soon as the animal begins to breathe, the lungs must at 

 once commence to function and, while, prior to birth, no blood 

 of any note has passed through the pulmonary arteries and capil- 

 laries, they must now promptly become active. In order that 

 the blood from the right ventricle shall pass through the pulmon- 

 ary arteries to the lungs, instead of through the ductus arteri- 

 osus into the aorta, it is essential that the latter becomes 

 promptly obliterated. 



The rupture of the umbilical cord finally interrupts the pla- 

 cental circulation and renders useless all those vessels within the 

 fetal body whose sole office was dependent upon the fetal circu- 

 lation. To this end, the intra-fetal portion of the umbilical 

 vein, with the ductus venosus, needs to close and disappear. 

 Vestiges of the umbilical vein persist, but its channel becomes 

 occluded within a very few da3'S after birth, unless interrupted 

 by disease processes. The allantoic, or umbilical, arteries must 

 likewise undergo a partial degeneration and complete loss of 

 function. When ruptured in the natural way, they usually part 

 just outside the abdomen, though some writers (Carsten- Harms) 

 allege that these arteries occasionally rupture within the ab- 

 dominal cavit}', especially in the cow. This is not wholly clear 

 and is .somewhat difficult of proof. In the foal, where it is 

 generally admitted that they divide outside the abdominal cavity, 

 the torn ends promptly retract within the bod}' and, dragging 

 with them the connective tissue surrounding their walls, 

 normally retreat from the surface in such a manner as to pre- 

 clude the possibility of hemorrhage and to greatly diminish any 

 danger from infection in these vessels. (See Fig. 56.) A 

 little later their ruptured ends retract to the vicinity of the 

 anterior portion, or fundus, of the urinary bladder, from whence 

 they may be traced throughout life as connective tissue cords, 

 passing from this point to the internal iliac arteries to constitute 

 the round ligaments of the bladder of the adult. 



