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PLACENTATION OF THE SEALS. 279 
umbilical vesicle was in contact with the placenta. The allantois conducted 
the umbilical vessels to the placenta, and enclosed them in folds, which formed 
meso-vascular bands, extending for a considerable distance around the inner 
face of the placenta. Folds of this membrane, also enclosing branches of the 
umbilical vessels, extended for some distance beyond the margins of the 
placenta, where they were so arranged as to form the walls of pouch-like 
recesses, which communicated with the general sac of the allantois. When 
this sac was first examined it seemed as if it was perfectly closed, and all com- 
munication between it and the urachus was cut off. But on. dissecting the 
tbdominal end of the cord I found a very slender tubular urachus, which was 
prolonged as a fine tube to open into the sac of the allantois, This tube 
possessed thin, semi-transparent walls, and was so fine that it barely admitted 
a pig’s bristle. It extended for 12 inch between the walls of the amnion and 
umbilical vesicle, and then for about the same distance between the apposed 
surfaces of the amnion and allantois, before it opened into the sac of the latter 
by a narrow funnel-shaped orifice, which was directed so obliquely as to form 
a valve-like arrangement. 
The amnion formed a large elongated bag, in which the foetus and liquor 
amnii were contained. It lay in relation to the concave aspect of the uterine 
horn, and the allantois was reflected around the greater part of its outer sur- 
face. Its sac was not equal in extent to the sac of the allantois, and the end 
which contained the tail of. the foetus was considerably smaller than the 
part in which the body and head were lodged. It was reflected in the usual 
way on to the umbilical cord, by which it was conveyed to the belly of the 
foetus. 
The short funis was cylindrical at its abdominal end, and contained a single 
vein, two arteries, and the tubular urachus. Two inches from its origin the 
vein bifurcated, and the cord became flattened, as the branches of the vein, 
each accompanied by an artery, diverged from each other. The arterial and 
venous trunks then subdivided into branches to reach thé placenta, invested by 
folds of the allantois as already described. In their course these branches 
passed between the allantoic membrane and the wall of the umbilical vesicle, 
and some even were suspended in the cavity of the vesicle. Branches both of 
the artery and vein ramified between the conjoined chorion and wall of the 
sac of the allantois, as far as the poles of the chorion. 
The umbilical vesicle, though very much smaller than the amnion, formed a 
well-defined sac which lay between the amnion and placenta, and was elon- 
gated laterally into two small horn-like prolongations, which ran parallel and 
in close relation to the narrower part of the placenta. Its outer surface was in 
part in contact with the allantois. A funnel-shaped prolongation passed up 
to the umbilical cord, as far as the angle of bifurcation of the two primary 
VOL. XXVII. PART III. 4D 
