358 ANATOMY AND PHYSIOLOGY 



Fig. 138 illustrates the way in which they are disposed in order 

 to provide for the increasing area to be supplied and for the 

 growth of the fetus. Their tortuous course provides for a greatly 

 increased distribution to constantly enlarging organs without 

 undue stretching of the vessels. 



During the first three or four months (according to different 

 authorities) the fetus is known as the embryo. 



Expulsion of the fetus during the first three months constitutes 

 abortion; from the fourth to the sixth months, it is called mis- 

 carriage. After six months it is possible for a strong fetus to go 

 on developing after expulsion (although exceedingly uncommon 

 at that date) ; therefore, from that time until term (the end of 280 

 days) expulsion constitutes premature delivery. The delivery of 

 the child is usually preceded by the escape of amniotic fluid. 



The quantity of amniotic fluid is about one liter. Its use 

 is to provide against injury from sudden jars or blows during 

 pregnancy, to allow freedom of movement on the part of the fetus, 

 to preserve the flexibility of the skin of the fetus, and at the time 

 of parturition to aid in the dilatation of the cervix of the uterus 

 as it fills a pouch of the amniotic sac which is forced down by 

 uterine contractions. 



Soon after the expulsion of the child, the placenta is separated 

 from its attachment to the uterus by the contracting walls and 

 later is expelled, with the ruptured and emptied sac. 



The placental site is now bare and bleeding. Large blood 

 spaces or sinuses are still open, left by the detachment of the pla- 

 centa, although rapidly closing if the uterus becomes well con- 

 tracted. 



Clinical note. The great advantage of a well-contracted uterus is, that 

 it guards against two possible dangers: (i) That of hemorrhage from the 

 open vessels; (2) (and even more serious if possible) that of infection through 

 this wide open surface. The latter is the reason for such scrupulous care 

 which is demanded in the nursing of obstetric cases. 



The lochia. The combined decidua vera and decidua reflexa 

 soften, disintegrate and come away from the uterus (with the blood 

 which is oozing from the interior) as lochia. The discharge is 

 known at first as the lochia rubra; then, when it is thinner, as the 

 lochia serosa. Third and lastly, when the disintegrated tissue cells 



