624 



DEVELOPMENT. 



[CHAP. XLIII. 



months of pregnancy. The contraction of the thick muscular 

 walls of the uterus tends to force the head upon the os uteri, in 

 consequence of which the circular fibres of the latter gradually 

 relax, and the opening dilates. The membranes are pressed 

 towards the vagina, and protrude through the os, until at length 

 they burst, and the liquor amnii escapes. 



At each successive pain, the child's head is forced lower and 

 lower into the vagina. The pains increase in force and frequency, 

 and the uterine contractions are assisted by the voluntary contrac- 

 tions of the abdominal muscles ; until at last, in a violent paroxysm 

 of pain, the head is born, and the remainder of the child very 

 quickly follows. 



A little haemorrhage usually occurs immediately after the birth 

 of the child, in consequence of the partial detachment of the pla- 

 centa. This is followed, however, by contractions ; and the placenta 

 itself is forced into the vagina shortly after the birth of the child. 

 "With the placenta are also expelled portions of the membrana 

 decidua, the remains of the chorion, and the ainnion. 



After labour, a considerable quantity of foetid discharge takes 

 place from the uterus. At first, this is composed principally of 

 blood; but afterwards it becomes paler, and consists chiefly of 

 mucus, with pus corpuscles, and a certain quantity of fluid exuda- 

 tion. The uterus gradually returns to its former volume. 



For information upon the questions discussed in the present chapter, the 

 student is referred to the works previously enumerated. 



