OBSTETRICS, OR MIDWIFERY 761 



uterine contractions which take place, together with 

 the pain incident to the same. 



Presentation and Position.— The term presenta- 

 tion has reference to the particular part of the body 

 which presents at the mouth of the womb. The term 

 position has reference to the location of the presenting 

 part in the passages of the mother. The most usual 

 presentation is the head. Occasionally the other ex- 

 tremity of the trunk takes precedence, forming what 

 is termed a ''breech presentation." In still other cases 

 the body lies crosswise of the outlet, a presentation 

 which must be modified in some way before the infant 

 can be born. 



There are various modifications of each of these 

 classes of presentation, that is, other parts of the head 

 ma}" present. In a perfectly natural labor, the vertex 

 of the head is the presenting part. 



Stages of Labor.— The labor is divided into three 

 stages : 



1. Dilation of the mouth of the womb. This is indi- 

 cated by cutting pains felt mostly in the back, contrac- 

 tions taking place in the womb only, and gradually 

 growing more and more frequent until the neck of the 

 womb is fully dilated. 



2. Expulsion of the child, by means of stronger con- 

 tractions, in which the abdominal muscles contract, as 

 well as the uterus. 



3. The expulsion of the after-birth. 



The average length of labor in women who have 

 previously borne children is about six hours, the first 

 four of which are occupied in the first stage, and the 

 latter two in the second stage. The after-birth is often 

 expelled at once after the expulsion of the child, but is 

 more often retained five to thirty minutes. 



