8 RICHARD ASSHETON AND THOMAS G. STEVENS. 
In region B there is a complicated system of wide blood 
channels (m. ch.), containing the maternal blood, and forming 
a series of interlocking loops around and between the foliations 
which contain the capillaries of foetal connection (f.c.) (fig. 2). 
The maternal blood flows in sinuous channels, having very 
definite walls, whose character we describe in a subsequent 
paragraph. 
Between the fibrous blood-vessel-carrying foetal plates and 
their foliations on the one hand, and the sinuous maternal- 
blood-carrying loops on the other, there is a well marked 
layer of tissue of a syncytial character which is present 
throughout, and which cannot from purely anatomical con- 
siderations be said to belong to the one or to the other. 
For reasons which will appear in the sequel we believe 
that it is wholly of foetal origin. 
This layer is not indicated in the diagrammatic fig. lL. 
Fig. 2, which is a careful camera drawing of a part of the 
region B, fig. 1, represents the histological nature of the 
parts just named. At fic. one of the terminal foliations of a 
foetal villus is thus seen in transverse section, the line ending 
in the fibrous groundwork, and at (c) a foetal capillary cut 
across transversely. Let it be noted that the size of the 
lumen is only just sufficient to accommodate a single red 
corpuscle. ‘hese capillaries, like all the foetal blood-vessels, 
are lined by a well marked endothelium. Occasionally a 
section will pass parallel to the flattened surface of the 
foliation and show the network of the capillaries (fig. 4). 
A maternal blood-channel packed with blood corpuscles may 
be seen at m.ch. These channels are loops of sinuous vessels 
which open into larger ones as indicated in fig. 2, m.ch. 
These channels have very well defined walls, but the walls are 
of a peculiar nature, and it is not possible to speak with cer- 
tainty about them without a knowledge of their development. 
The walls are homogeneous, with a thickness of about 
3 diameter of a red corpuscle. They stain with the same 
dyes that stain the fibrous tissue of the fcetal villi, but less 
strongly. We believe the walls to be quite devoid of nuclei; 
