PROFESSOR TURNER ON THE PLACENTATION OF THE SLOTHS. 79 
subdivided. By snipping out specimens along with surrounding placental sub-~ 
stance with a pair of fine scissors, and then teasing out the preparation with 
needles, on placing the object under a low power of the compound microscope, 
I could follow these branches for some distance. In one specimen I observed 
that the vein immediately after penetrating broke up at once into a penicillar 
cluster of branches (fig. 7). In another specimen the branches arose after 
the arborescent plan. When several of these branches were traced onwards 
into the placental substance, they were seen to lose their originally straight 
direction, and to become very convoluted (fig. 8). The coats of the veins 
were not so brittle as those of the arteries, so that these vessels could be 
followed for a longer distance with comparative ease. I may further mention 
that the lobes were well injected with the red gelatine in the immediate vicinity 
of the localities where they were penetrated by the maternal vessels. 
It now became a matter of much importance to trace the maternal vessels 
further into the placental substance in order to ascertain their arrangements 
within the lobes, and their relations to the foetal villi. As the intra-placental 
branches, both of the curling arteries and utero-placental veins, were too small 
to be followed out to their termination by the ordinary means of dissection, thin 
slices were then removed from some of the lobes, after hardening in spirit, with 
the aid of STIRLING’s section-cutter, and submitted to examination under both 
the lower and higher powers of the microscope. 
In vertical sections made through the thickness of a lobe from the chorionic 
to the decidual surface, the intra-placental maternal vessels presented a very re- 
markable and characteristic appearance, which differs in various particulars from 
any that I have either seen or read of in other animals. These vessels were 
many times larger than capillaries, and possessed a transverse diameter varying 
from ‘003 to ‘008 inch (fig. 4). Their course was serpentine or even convoluted, 
and as they wound in and out between the villi, sometimes bending at an acute 
angle, at others possessing a more gentle curve, they had been repeatedly cut 
through by the razor in the plane of section; sometimes a maternal vessel was 
divided for a considerable distance, relatively speaking, parallel to its long axis, 
at others it was cut obliquely, at others transversely. Sometimes adjacent con- 
voluted vessels anastomosed with each other, and here and there an appearance 
resembling a varicose dilatation of the wall of the vessel was recognised ; but it 
is possible that these apparent varicosities in some instances may have been 
due to the cut having passed very obliquely through a main vessel at the origin 
of one of its branches. Under a low power, it not unfrequently seemed as if 
a convoluted vessel had extended so parallel to the plane of section, that a very 
considerable length of it had been exposed as a continuous undivided tube ; 
but when a higher power was employed, and a more perfect definition of the 
VOL. XXVII. PART I. Xx 

