yS INTRODUCTION TO SKXUAL PHYSIOLOGY 



torn away, but very occasionally there is an intact hymen, even 

 after parturition. Typically the back of the head is turned 

 towards the pelvic symphysis. The bones of the head are some- 

 what compressible, and there is generally just sufficient room 

 for it to pass through the bony pelvic ring without undue strain. 

 Very occasionally the head is too big to traverse the passage 

 and the child's life may have to be sacrificed to preserve that 

 of the mother. The body of the foetus passes out more easily, 

 for the shoulders are more readily compressible. The umbilical 

 cord by w^hich the child is attached to the placenta is severed by 

 the attendant about 1 or 2 inches from the child's navel ; 

 the child then begins to breathe and frequently emits a cry. 

 Its body is almost completely covered by the lanugo hair, which 

 comes away shortly after, together with a certain number of 

 dead epidermal cells and products of secretion from the skin. 

 The birth of the child marks the end of the second stage of labour. 

 As soon as the child is born the remainder of the amniotic fluid 

 escapes, and this is usually stained wdth blood. 



The uterine contractions then cease, but are renewed after 

 a short but somewhat variable interval. As a result of the 

 contractions the placenta or after-birth is first separated from 

 the interior of the uterus and then passed into the vagina, 

 whence it is finally expelled by the action of the muscles of 

 the abdomen. During this process, which constitutes the third 

 stage of labour, there is some bleeding, the quantity of blood 

 lost being, on an average, about 300 c.c, or rather less. 

 The further contractions of the uterus gradually facilitate the 

 closing of the torn blood vessels. The foetal membranes are 

 expelled with the placenta and also the remainder of the 

 umbilical cord which is attached. 



The duration of labour is about six hours longer in the case 

 of first pregnancies than in later ones. In the former the three 

 stages take about sixteen hours, two hours, and a quarter of 

 an hour respectively, and in the latter eleven hours, one hour, 

 and a quarter hour. At the commencement of labour the 

 "pains" occur at intervals of about fifteen to thirty minutes 

 and gradually become much more frequent so as to take place 

 every two or three minutes. Each contraction lasts from thirty 

 to ninety seconds, but the actual sensation of pain is consider- 

 ably briefer. The force exerted at each contraction is very 



