354 REPRODUCTION 



effectually check the hemorrhage which separation of the pla- 

 centa occasions. 



Umbilical Cord. The umbilical cord is made up of the 

 vessels which convey blood between the placenta and fetus, to- 

 gether with the remnants of the umbilical vesicle and allantoic 

 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 allantoic 

 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 frondosum) and 

 become now the umbilical vessels. The two veins blend to 

 constitute a single umbilical vein, but the arteries remain sep- 

 arate. The vein enters the fetal body at the umbilicus, passes 

 to the under surface of the liver and divides in a manner to be 

 noted presently. After birth the intra-abdominal portion 

 atrophies, and is the round ligament of the liver. The two 

 umbilical arteries issue at the umbilicus. Their intra-abdominal 

 portions are the fetal hypogastric arteries. 



The average length of the umbilical card 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 without 

 inward, the decidua vera, decidua reflexa, chorion and amnion. 

 The amniotic fluid, in which the fetus floats, reaches its maxi- 

 mum amount at about the sixth month. It is sufficient then to 

 force the amnion closely against the chorion, covered by the 

 decidua reflexa; these last named (chorion and reflexa) are in 

 turn forced everywhere against the decidua vera. The result 

 is that all four become practically one membrane, though the 

 union between amnion and chorion is not so close as that between 

 the other layers. These membranes constitute, then, a sac 



