No. 3.] UTERUS AND EMBRYO. 391 
out mesoderm; 2°, a thick bud with a well-developed core of 
connective tissue, and having a nearly cylindrical form. Between 
these extremes every intermediate state can be found. Other 
observers have noted this peculiar manner of growth, which I 
have found still going on in the placental chorion during 
the fourth month. Robin, 125, appears also to have crudely 
observed both the young hollow villi, and the solid epithelial 
buds. The blood-vessels he traces to the division of the cavity 
of the villi into an artery and a vein; from the nature of things 
he offers no observations in support of this assertion. 
Only the tips of the villi touch 
the surface of the decidua, 
either at first or subsequently, 
except of course, over the cho- 
rion lave during the abortion of 
the vill. ~ The tips’ of the villi 
are attached to the uterine sur- 
face; they penetrate the decidua 
for a short distance, but even in 
the placental area at the close 
of gestation, the penetration is 
slight, and the villi make their 
way only into the surface stratum 
of the decidua serotina. There 
is no evidence of any sort that ae 2 . 
. . :. yy i] 
the villi penetrate the glands she 
at any period. The relation of Cut 73.—Isolated terminal branch 
of a villus from the chorion of an em- 
the villi to the decidua has now iyo afl twelve ween 
been so accurately ascertained, 
that there can be, I think, no longer any question whatso- 
ever on this point. The best discussion is by Langhans, 110, 
Py 2o tik. 
The shape of the villi varies according to the part of the 
chorion and the age of the embryo. They gradually abort over 
the chorion leve, and gradually grow over the chorion frondo- 
sum. Let us begin with the placental villi: At first they are 
short, thick-set bodies of irregular shape, as shown in Cut 12; at 
twelve weeks their form is extremely characteristic, Cut 13; the 
main stem gives off numerous branches at more or less acute 
angles, and these again, other branches, until at last the termi- 
