vi PEEGNANCY PAETUEITION PUEEPEEIUM 245 



to enable it to live detached from the maternal organism, is very 

 similar to that by which .the last portion of the intestine and 

 the bladder, which are both contiguous to the genital canal, are 

 emptied. 



In these acts, as in parturition, the expulsive or ecbolic work 

 is effected by contractions of the smooth muscular fibres, forming 

 the walls of the muscular cavities, aided by abdominal pressure, 

 that is, by contractions of the muscles of the abdominal wall and 

 the diaphragm. Notwithstanding the development attained by 

 the body of the new individual in the higher animals and in man, 

 its separation from the mother may be effected under physiological 

 conditions without any artificial aid, and without injury to either 

 mother or child, when the presentation is occipital, which is the 

 case in about 95% of births. 



The expulsive forces which determine parturition are specially 

 due to peristaltic contractions of the smooth muscles of the uterus, 

 assisted more or less by activity of the striated muscles in the 

 production of abdominal pressure. The uterine contractions are 

 usually accompanied by more or less painful sensations which 

 are called pains, and are localised mainly in the sacral and lumbar 

 regions, and later on extend to the region of the fundus of the 

 uterus. The pains begin when the contractions assume a certain 

 intensity, their severity increasing in proportion to the strength 

 of the contractions. 



The uterine contractions, like all those of smooth muscles, 

 are independent of the will; their peristaltic character, that is 

 their direction towards the outlet of the genital canal, cannot 

 be perceived in the uterus of woman, owing to the rapidity with 

 which they spread, but may be observed distinctly in the uterine 

 cornua of animals, in which the contractions begin at the extreme 

 end of the tube and spread like waves towards the external orifice 

 of the uterus. 



The contractions and the pains accompanying them have 

 three stages, increment, acme and decrement. They last one 

 minute on an average and are followed by a longer pause of 

 muscular relaxation. The pauses between two successive pains 

 last at first ten to fifteen minutes; later they become shorter, 

 and towards the end of parturition succeed one another every 

 minute or thirty seconds. 



During the contractions there is an increase of intra-uterine 

 pressure uniformly distributed both on the amniotic fluid and 

 on the body of the foetus ; this pressure Schatz has succeeded in 

 measuring with a suitable manometer (Fig. 105). 



We have as yet no clear or adequate knowledge of the innerva- 

 tion of the uterus. 



The majority of the nerves of the uterus are of sympathetic 

 origin, but cerebro-spinal fibres are not wanting. As may be 



