80 PROFESSOR TURNER ON THE PLACENTATION OF THE SLOTHS. 
wall of the vessel therefore obtained, it was seen that the tube, owing to its 
tortuosity, had been cut across more than once, and that, instead of possessing 
an unbroken continuity, a series of oblique or transverse sections through its 
walls had been obtained. 
It might have been supposed that the maternal vessels, in their course from 
the decidual to the chorionic aspect of the placenta, would have diminished in 
size, so that their diameter near the former surface would invariably have been 
greater than in the region of the latter ; but this was not found to be the case. 
For although the main branches of the arteries and veins were necessarily 
nearer the decidual aspect, yet along with these were smaller branches of about 
the same calibre as those found close to the surface of the chorion. 
I then proceeded to examine the intra-placental maternal vessels, with the 
view of ascertaining if they possessed definite walls capable of being isolated 
from the villi between which they lay; or if they were merely a freely anas- 
tomosing or cavernous system of blood spaces, which either did not possess 
definite walls at.all, or whose walls were incorporated with the tissue of the villi. 
That the intra-placental branches, arising directly from the curling arteries and 
utero-placental veins, possessed distinct walls, there was no difficulty in at once 
deciding, as their coats could be traced in continuity with those of the trunks 
from which they arose, and they could be readily separated from the surround- 
ing structures; but the serpentine and convoluted vessels continuous with these 
branches, on account of the mode in which they were intermingled with the villi, 
required to be more closely examined. I proceeded to study them under the 
microscope, both in sections through the lobes, where they were as far as possible 
in situ, and also in teased-out preparations, and from both methods of examination 
I obtained ample proof that these vessels possessed a definite wall. In thin 
sections, even when no displacement of the relative positions of the villi and con- 
voluted maternal vessels had taken place, a limiting membrane, distinct from the 
tissue of the villus, could be traced around the vessels, whether they contained 
injection or not,more especially when they were transversely or obliquely divided ; 
and the presence of an independent wall of the vessel was naturally more clearly 
seen when some displacement of a vessel from the villi between which it had 
originally been placed had occurred. In preparations teased out with needles, 
the structure of the wall of the tortuous vessels could be studied. It was of 
great delicacy, possessed no elastic tissue or muscular fibre-cells, and seemed 
to consist essentially of a nucleated protoplasm, in which faint traces of fibrilla- 
tion were recognised. In one specimen I was so fortunate as to obtain, after 
the addition of acetic acid to an uninjected vessel, a demonstration of a delicate 
but perfectly distinct endothelial lining, the cells of which were ovoid in shape, 
with smooth and not jagged edges, and in some cases with nuclei in their 
interior (fig. 10). 
- —— ae 
