78 PROFESSOR TURNER ON THE PLACENTATION OF THE SLOTHS. 
was retained on the placenta was the deciduous serotina properly so called. 
The tissue torn through resembled in its naked-eye appearance the decidual 
layer which connects the human placenta to the uterine wall; and the surfaces 
which had been in apposition were smooth and without either pits or villi, such 
as one sees in stripping off a diffused or cotyledonary placenta from the cor- 
responding uterine area. When the non-deciduous serotina was removed, the 
thin muscular wall of the uterus was exposed. In microscopic structure, both 
the deciduous and non-deciduous serotina consisted of a very delicate connective 
tissue, in which the corpuscular element was large and distinct, though the cells 
did not assume either the size, or the proportion as regards numbers, of the 
colossal cells of the human serotina. In the former a very large number of plate- 
like crystals were seen after the placenta had been hardened in spirit. 
The Serotina was not, however, the only structure exposed in the course 
of this dissection; for the arteries and veins proceeding to and from the 
placental lobes were distinctly recognised (fig. 2). Each lobe had at least one 
artery penetrating its uterine surface ; sometimes the artery entered the centre 
of a lobe, at others nearer its margin. ‘These arteries corresponded to the 
curling arteries of the human placenta, and possessed a very characteristic 
appearance as if twisted into a close spiral. Usually the curling artery and 
vein connected with a given lobe penetrated it at some distance from each 
other, but in one instance I saw them enter close together. I traced more than 
one of these arteries into their respective lobes, and found that the artery 
branched immediately on entermg. In two cases it divided into three branches, 
and these again subdivided into smaller arteries. But it should be stated that 
the branches did not possess the twisted form of the trunk from which they 
proceeded ; and owing to the brittleness of their coats, they readily tore through 
in the act of dissection. 
One, and sometimes two, venous trunks, uniform in size with the curling 
arteries, left each placental lobe, usually near the margin. ‘They differed from 
the arteries in being smooth and free from the peculiar twisted appearance, 
though in tracing them obliquely through the non-deciduous serotina and the 
muscular coat it was not uncommon to find them pursue a serpentine course. 
Those veins which proceeded from the lobes lymg near the broad ligament 
passed obliquely through the muscular wall of the uterus into a venous plexus 
in that ligament. It is important to note that neither in the decidua serotina 
nor in the muscular wall of the uterus did these veins dilate into sinuses: in 
both localities they preserved the tubular, cylindrical form. Usually the veins 
lay for some distance partially imbedded in grooves on the uterine face of the 
lobes, and subdivided into two or more branches before they penetrated their 
substance. By a little careful dissection, I was able to follow these branches 
into the lobes, and to see that immediately after entering they again rapidly 
