286 MR. R. ASSHETON ON THE F@TUS AND [June 6, 
blood makes up nearly half the thickness of the placenta, and 
contains no foetal mesoblast or blood. 
The half of the placenta towards the feetal surface is made up 
of trophoblast (much attenuated) forming channels filled with 
maternal blood, which take a more or less sinuous course, and a 
network of fine fatal capillaries, with also the larger vessels and 
larger main maternal channels. This is shown diagrammatically 
in text- fig. 45, FC, p. 285). 
Text- fig. 43 (p. 283) is a drawing of an actual section of a piece 
of this region near the maternal surface. The great bulk is made 
up of the ‘channels (MCH) excavated in the trophoblast containing 
maternal blood. There are many leucocytes (LE), The walls of 
these channels are thin, though the large trophoblastic nuclei (T) 
are very conspicuous. The feetal capillaries are seen at F.BY. 
Nearer to the feetal surface the maternal channels become 
finer and the feetal capillaries perhaps rather more numerous. 
At places where the main feetal arteries penetrate the tissues of 
the placenta, a considerable quantity of foetal mesoblast tissue 
accompanies them. 
There are a few spherical masses of tissue within this region, 
which are not vascular, nor do they seem to be trophoblastic. 
They resemble in some respects Duval’s “ilots vésiculeux,” which, 
according to him, are pieces of the maternal sub-mucosa which 
have become enveloped by the advancing trophoblast layer. 
The main features of the vascular systems are fairly easily 
determinable. 
In this specimen the whole of the maternal arterial blood- 
supply arises from a single artery in the centre (MA), which 
opens into the large afferent channel which lies partly in the 
trophospongial tissue and partly in the trophoblast. 
This, like the other main channels, is lined by a flattened 
epithelium-like layer, which is probably a pseudo-epithelium of 
trophoblastic origin where the wall is trophoblast, and tropho- 
spongial origin where the wall is trophospongia. 
Duval has described the growth inwards along the maternal 
vessels of trophoblast cells to form a pseudo-epithelium. This is 
denied by Jenkinson*, who derives the pseudo-epithelium from the 
simple flattening of the adjacent cells. This is not a question 
which can be decided by reference to a single stage; but I may 
say that there is nothing in this specimen which supports in any 
way Duval’s account in the mouse. 
The afferent channel divides into two main branches, which 
diverge and then penetrate straight to the fcetal surface of the 
placenta. Here they break up into channels, which take a rather 
more sinuous course back again to the middle of the thickness of 
the placenta, where they collect into a number of efferent channels 
lying near the surface of the trophoblast and ultimately into two 
* Jenkinson, J. W., “ Observations on the Histology and Physiology of the Placenta 
of the Mouse,” Tijdschr. d. Ned. Dierk. Vereen. DI. vn. 1902. 
