CIRCULATION OF BLOOD IN THE FETUS 



73 1 



blood of the fetus is enriched and purified after the fashion necessary for the 

 proper growth and development of those parts which it is designed to nourish. 

 The whole of this structure is not, as might be imagined, thrown off 

 immediately after birth. The greater part, indeed, comes away at that time, 

 as the after-birth; and the separation of this portion takes place by a rending 

 or crushing through of that part at which its cohesion is least strong, namely, 

 where it is most burrowed and undermined by the cavernous spaces before 

 referred to. In this way it is cast off with the fetal membrane. The remain- 



FIG. 503. Diagrammatic View of a Vertical Transverse Section of the Uterus at the 

 Seventh or Eighth Week of Pregnancy, c, c, c', Cavity of uterus, which becomes the 

 cavity of the decidua, opening at c, c, the cornua, into the Fallopian tubes, and at c' into the 

 cavity of the cervix, which is closed by a plug of mucus; dv, decidua vera; dr, decidua 

 reflexa, with the sparser villi embedded in its substance; ds, decidua serotina, involving 

 the more developed chorionic villi of the commencing placenta. The fetus is seen lying 

 in the amniotic sac. The umbilical cord and its vessels pass up from the umbilicus to 

 the distribution of the blood vessels in the villi of the chorion- and the pedicle of the 

 yolk-sac the cavity between the amnion and chorion. (Allen Thomson.) 



ing portion is either gradually absorbed, or thrown off in the uterine dis- 

 charges which occur at this period. A new mucous membrane is of course 

 gradually developed. 



Circulation of Blood in the Fetus. The circulation of blood in the 

 fetus differs considerably from that of the adult. 



Returning from the placenta by the umbilical vein the blood is first con- 

 veyed to the under surface of the liver, where the stream is divided a part of 



