348 
PEOEESSOE OWEN ON THE E(ETAL iMEHBEANES 
and are of a relatively coarser character. The greater part of the outer convex surface 
of the placenta is smooth ; the rough surface, which had been tom from the maternal or 
uterine placenta, exposed the foetal capillaries, and occupied chiefly a narrow tract (c. c) 
near the middle line of the outer surface. A thin brown deciduous layer is continued 
from the borders of the placenta, for a distance varying from 1 to 3 inches, upon the outer 
surface of the chorion. Flattened folds of a similar substance, or false membrane, could 
be raised from some parts of the surface of the placenta ; at other parts the substance 
formed irregular flbrous bands, the flbres extending in the dfrection of the circum- 
ference of the placental ring. The outer smflace of the chorion is for the most part 
smooth and shining ; but at each of the obtuse extremities of the sac there was a vil- 
lous and vascular subcircular patch (d, d), between 2 inches and 3 inches in diameter, 
the villi being short and graniform, ^th of a line in diameter, or less. Thus the chief 
points of attachment of the chorion to the uterus are, at the equator, by the annular 
placenta, and at each pole of the elongated sac, by the subcircular 'cillous patch. 
The umbilical cord (f), formed by one venous and two arterial trunks, and by the 
slender neck of the allantois, with the connecting cellular tissue and the covering of 
amnios, is short and somewhat flattened. It measm’ed about 6 inches in length, before 
the division of the vascular trunk, and about 3 inches in cfrcumference. 
The inner surface of the amnios is roughened by brownish hemispherical granules, 
from one line to of a line in size, commonly about half a hne ; the outer smdace is 
flnely wrinkled, hut smooth. The amnios is continued from the base of the umbilical 
cord upon the allantois, which is of considerable size, and is so interposed between the 
chorion and amnios, as to prevent any part of the amnios attauiing the inner surface of 
the placenta. The amnios consists of two layers : one is the granular layer, continued 
upon the inner or foetal surface of the allantois, and thence upon the umbihcal cord ; 
the other is the smooth outer layer, continued upon the outer or choiional surface of the 
allantois, and thence upon the inner surface of the chorion. 
The allantois, into which the urachus (g) at the torn foetal end of the cord rapidly 
expands, divides, where the amnios begins to be reflected upon it, into tlmee saccuh : one, 
which is the largest, extends over the inner surface of the annular placenta, and projects 
a little way into the unruptured sac of the chorion (a) : a second division or horn of the 
allantois extends into the opposite or ruptured sac of the chorion («'), whence the foetus 
had escaped ; it there bends round towards the placenta, and its apex adlieres at that 
part to the first division of the allantois: the thfrd prolongation subdi-^ides into two 
smaller cavities, each terminating in a cul-de-sac, encompassing, and closely attached to 
the primary divisions of the umbilical vessels. The line of adhesion of the amnios to the 
allantois, where it is reflected upon these cul-de-sacs, measures 3 feet 6 inches. 
The umbilical vein, at the distance of 6 inches fi’om the torn or foetal end of the cord, 
divides ; and, 3 inches farther, one of the branches subdirfdes. The fii’st dirfsion of the 
umbilical arteries takes place 9 inches from its torn extremity. The primary branches 
of the umbilical arteries and vein diverge from the umbilical cord in fom* dirfsions. 
