PARTURITION 363 



the mother to the offspring, and the waste products from 

 the offspring to the mother. It is important to reahse 

 that there is no mixing of the maternal and foetal blood. 



The growth in size of the uterus as pregnancy proceeds 

 is due largely to the elongation and thickening of the 

 muscle fibres. 



PARTURITION 



Pregnancy lasts about 280 days and is terminated by 

 the expulsion of the foetus. Throughout pregnancy the 

 uterus undergoes shght contractions which are not felt 

 by the mother. As the uterus reaches its maximum growth 

 these contractions become gradually stronger and more 

 frequent. At the onset of labour they increase further 

 in intensity and frequency, and are accompanied by pain 

 which eventually becomes extreme. Labour is technically 

 divided into three stages. The first is the dilatation of 

 the OS uteri, due to contraction of the longitudinal uterine 

 muscles. The second is the expulsion of the foetus. The 

 tliird is the detachment of the placenta from the uterine 

 wall and its expulsion. The second and third stages are 

 brought about by the combined contraction of the longi- 

 tudinal and circular muscles of the uterus and of the muscles 

 of the abdominal wall. As the contents of the uterus become 

 smaller the uterine muscles after each contraction remain 

 at their shortened length. 



Parturition can occur in animals after section of the 

 thoracic region of the cord, and in women suffering from 

 complete paralysis of the lower limbs. For its proper 

 performance the integrity of the lumbar part of the cord 

 appears to be essentia], but in some animals it occurs, though 

 often imperfectly, after complete destruction of the lower 

 part of the cord. Under these circumstances parturition 

 occurs through the uterine contractions only, the abdominal 

 muscles play no part. Normal parturition is therefore 

 due partly to the inherent rhythmicity of the uterus and 

 partly to reflex contraction. The function of the spinal 



