1888.] Dr Berry Hart on Separation of the Placenta. 429 
glands of the mucous membrane of the unimpregnated uterus, which 
has, as the result of conception, become the decidua vera. 
The placenta, viewed in the same aspect, is made up of two 
portions separated by a spongy layer. Towards the uterine cavity 
we have the part made up of amnion, chorion, chorionic villi with 
intervillous spaces between, and the portion of the serotina known 
as the large-celled layer. 
On the uterine side of the placental spongy layer we get a part of 
the serotina lying on the uterine wall. The spongy layer in the 
placenta has an origin similar to that in the membranes, as the 
spaces are lined by columnar epithelium. 
There is thus in the membranes and placenta a spongy layer, each 
lying in the same plane, and therefore continuous, forming a line of 
cleavage, at which the membranes and placenta will he separated as 
the result of labour. 
If we now look at the uterus after labour has gone on for some 
time, we find a remarkable change has taken place in its divisions. 
The lower uterine segment and cervix have now become canalised, 
and together make a tube measuring 10 cm. in all its diameters. 
By the end of the first stage we get the membranes in the lower 
uterine segment separated by a tearing of the traheculse already 
alluded to, and this separation is caused in the following manner : — 
As the result of the uterine pains, and the deeper passage of the 
child’s head, the area of the lower uterine segment is increased. Of 
the membranes, only the amnion is driven on and expanded, a 
condition allowed by the loose union of the amnion to the chorion. 
The increase in area of the lower uterine segment is not partici- 
pated in by the deciduae, owing to the loose spongy layer, and 
we thus get a disproportion between the site of the attachment 
of the deciduae and the deciduae themselves, a disproportion causing 
tension of the trabeculae sufficient to tear them — ^.e., to cause 
separation. 
While this explains the separation of the membranes in the lower 
uterine segment, we have now to consider how the membranes and 
placenta, placed above the contraction ring, are separated during 
the third stage. The conditions here are different, as the lower 
uterine segment is passively stretched during labour, while the 
uterus above the contraction ring actively retracts and relaxes, and 
