2i8 NORMAL PARTURITION. 



as well as more continuous. Not unfrequently they are more powerful in 

 weak-looking animals than in those which are robust and vigorous ; and 

 their energy depends evidently upon the development of the muscular 

 structure of the uterus, and the potency of the sympathetic ganglia which 

 stimulates it. Their energy and frequency also often depend upon the 

 duration of the pains, and the existence of mechanical obstacles to the 

 birth of the foetus. 



After the complete dilatation of the os, the third stage of delivery 

 begins, and the manner in which the uterus contracts is modified. The 

 resistance is no longer at the cervix, but in the uterus itself, being due to 

 the presence of the foetus ; and now the circular as well as the longitudi- 

 nal fibres come into action simultaneously, in order to diminish the 

 uterine cavity and quite expel its contents. In this they are greatly aided 

 by the abdominal muscles and the diaphragm, which until now could 

 assist but little ; though the participation of these does not appear to be 

 absolutely indispensable, for birth may take place without it. Neverthe- 

 less, it is a fact that in diminishing the abdominal cavity, and pressing 

 on its contents, these muscles concur in pushing the foetus in the direc- 

 tion in which least resistance is offered — towards the pelvic cavity ; and 

 as their contractions are effective, so do those of the uterus, which are 

 coincident with them, become increased in power and frequency. The 

 animal "strains," as in defecation or micturition, but with all its force; 

 and these throes, which are involuntary to a great extent, and in which 

 nearly all the muscles of the trunk share, soon bring the act to a termi- 

 nation. 



The foetus itself has been sometimes regarded as the chief agent in 

 parturition, from the fact that this act is Jonger and more difficult when 

 the creature is dead, and that it has been expelled after the mother has 

 ceased to live. But it must be remembered that the movements of the 

 foetus are very trifling, and of little importance when compared with the 

 resistance to be overcome at birth ; so that the young creature must 

 remain almost, if not quite passive during the act. And if this act is 

 tardily accomplished- when the foetus is dead, the delay maybe due to the 

 absence of stimulation or irritation in the organ, to the uterus not having 

 a fixed point to act upon, or perhaps even to a local septosis or paralysis 

 from the decomposition of the foetus. 



With regard to expulsion of the foetus after the death of the mother, it 

 must also be remembered that all the organs do not cease to live at once, 

 and that many continue to contract for some time after the mother's 

 heart has ceased to pulsate. Leroux has felt this organ contracting a 

 quarter of an hour after death, and after gastro-hysterotomy on the dead 

 human body it has been seen to contract as in the living woman ; Haller 

 has witnessed the contraction of the cornua of the Cat's uterus, even 

 when the organ was detached from the body; and Colin states that he 

 has observed the uterus of Sheep to contract for forty and fifty minutes 

 after death. 



As we have said, the resistance which the expelling forces have to 

 overcome is constituted by the foetus and its membranes, and the genital 

 passages — the os uteri, vagina, vulva, as well as the pelvis and soft parts 

 covering and lining it. The foetus participates in the resistance by its 

 volume, its form, its manner of presentation, its position, the conforma- 

 tion and texture of the tissues which unite it to the mother, etc. ; while 

 the genital passages offer resistance from their form, width, extensibility, 



