724 UTEROGESTATION, 



moving through the ^vhole of the placental spaces in contact with or 

 in closest proximity to the foetal villi, it is returned by numerous veins 

 through the outer decidua serotina into the vascular channels of the 

 uterus. This blood is essentially arterial in its qualities, and may be 

 supposed to perform a double function, viz., 1. to exert an aerating 

 effect on the blood of the foetus through the tissue of the villi and the 

 walls of their minute vessels, and 2. to supply for absorption by the 

 foetal vessels the new materials required in the continued nourishment 

 of the foetus. 



The continuity of the decidua vera and decidua reflexa with the 

 decidua serotina, and of all three with the whole thickness of the 

 placenta at its margin, sufficiently demonstrates the actual coonection 

 of the maternal elements in these several structures, and the existence 

 of that connection is fully confirmed by tracing the steps of the primary 

 formation and subsequent development of the two sets of placental 

 elements, by which are ascertained the actual presence of both in the 

 commencement, and the gradual modification and disappearance of the 

 maternal part. The view thus arrived at receives further support from 

 the result of the observation of the varieties of form and structure 

 presented by the placental organisation in different animals. 



Separation at Birth and Restoration of the Mucous Mem- 

 "brane of the Uterus. — In the act of birth the whole decidual struc- 

 tures which have been formed in human uterogestation are separated from 

 the uterus along with all those belonging to the ovum, and the placenta- 

 tion is thus said to be completely deciduate. Thus in parturition, fi'om 

 the effect of the contraction of the uterine walls and the abdominal 

 muscles, after the usual rupture of the foetal membranes and the dis- 

 charge of the amniotic fluid, the foetus is first expelled : the placenta is 

 next detached and pressed downwards, carrying with it the layer of 

 serotina by which it is covered on its uterine surface, and along with 

 it necessarily are broken through the coiled arteries and the slanting 

 veins ; the membranes of the ovum follow, consisting of the amnion 

 and chorion, together with the shrunken covering of decidua which in 

 the last stage of pregnancy remains from the union of decidua reflexa 

 with decidua vera matted together into one, which is finally peeled off 

 the whole of the interior of the uterus. 



The uterus having now contracted and its cavity being greatly reduced 

 in size, there remains, probably, on the uterine surface a part of the sub- 

 epithelial or decidual structure of the mucous membrane, in irregular 

 shreds rather than in one continuous layer, and in the deeper part are 

 imbedded the convoluted uterine glands extending outwards into the 

 layer of fibres formed by the muscularis mucosse. These remains of 

 decidua, with the clots of blood resulting from the rupture of the 

 vessels, are gradually cast off with the lochia, a discharge which is at 

 first of a mixed character, but gradually becomes more and more com- 

 posed of corpuscles similar to the white blood globules, and this is 

 succeeded by the closure and contraction of the vessels, the prolongation 

 of the gland tubes to the surface, the formation of a complete ciliated 

 epithelial lining to the cavity, and the complete restoration of the 

 natural structure of the whole membrane. 



