UMBILICAL CORD 355 



At labor uterine contractions detach the placenta and the 

 decidua and expel them from the womb. The separation 

 takes place in the deeper part of the maternal placenta, or 

 decidua serotina, so that the mass discharged represents both 

 the fetal and maternal portions. The vessels entering the 

 sinuses do so obliquely ; consequently uterine contractions at 

 birth very effectually check the hemorrhage which separa- 

 tion of the placenta occasions. 



Umbilical Cord. The umbilical cord is made up of the 

 vessels which convey blood between the placenta and fetus, 

 together with the remnants of the umbilical vesicle and allan- 

 toic stalk, all of which are held together by the jelly of 

 Wharton, a species of connective tissue. 



The outgrowing allantois has developed in it the two al- 

 lantoic arteries and veins. By the time the placenta is 

 formed the allantoic stalk has become much elongated, and 

 the allantoic vessels extend into the fetal placenta (chorion 

 f rondosum) and become now the umbilical vessels. The two 

 veins blend to constitute a single umbilical vein, but the ar- 

 teries remain separate. The vein enters the fetal body at the 

 umbilicus, passes to the under surface of the liver and di- 

 vides in a manner to be noted presently. After birth the 

 intra-abdominal portion atrophies, and is the round liga- 

 ment of the liver. The two umbilical arteries issue at the 

 umbilicus. Their intra-abdominal portions are the fetal hy- 

 pogastric arteries. 



The average length of the umbilical cord is about twenty- 

 one inches. It appears to be twisted on account of the spiral 

 course of its relatively long arteries. It is usually attached 

 near the center of the fetal surface of the placenta. 



Condition of the Fetal Membranes at Birth. The mem- 

 branes discharged with the placenta at birth are, from with- 

 out inward, the decidua vera, decidua reftexa, chorion and 

 amnion. The amniotic fluid, in which the fetus floats, 

 reaches its maximum amount at about the sixth month. It 

 is sufficient then to force the amnion closely against the cho- 



