PLACENTATION OF THE SEALS. 301 
systems of the blood-vessels, but by the production of a secretion in the 
maternal placenta which is absorbed by the foetal placenta. The great vascularity 
of the maternal placenta is in relation therefore to the activity of this new 
formed glandular organ, and to the amount of the pabulum required for the 
production of the secretion. 
EXPLANATION OF PLATES. 
Figures 1, 2, and 3 were drawn from nature under my superintendence by Mr Prrer THomson; 
Figures 4 and 9 by Mr Joun R. Ret. For the series of beautiful microscopic drawings from which 
the remaining figures have been engraved, I am indebted to my former assistant, Mr J. C. Ewart, M.B. 
Puate XVIII. 
Figure 1. Gravid uterus, vagina, broad and round ligaments, ovaries, and bladder of Halichwrus gryphus. 
Ut, uterus; V, vagina; O, left ovary; B, bladder. Figures 1, 2, 3 much reduced. 
Figure 2. Gravid uterus of the same animal, the cavities of which and of the vagina have been opened 
into. Ut, the wall of the uterus in the region of the zonary placenta; the shaded tringe 
on each side is to represent the free edge of the placenta. Ch, ch, the non-placental part of 
the chorion; m, the non-gravid horn of the uterus, into which the foetal membranes do not 
extend; V, the vagina, into the cavity of which the cervix uteri may be seen projecting. 
Figure 3. A view of the foetal membranes which have been everted. PI, the inner convoluted surface 
of the placenta, which is traversed by folds of the allantois, containing branches of the 
umbilical vessels; al, al, the inner surface of the allantois; am, the sac of the amnion’ 
opened into, out of which the foetus has been removed; w, the short umbilical cord; wz, 
one of the two horns of the umbilical vesicle, the opposite horn is concealed between the 
right pole of the amnion and the placenta. 
Figure 4. Vertical section through the wall of the uterus and placenta at and near the margin of the 
latter. Ut, wall of the uterus, in which the large uterine vessels may be seen; Pl, the 
placenta; ds, decidua serotina, passing from the inner surface of the uterus into the sulci 
between the convolutions of the placenta; m, the mucous membrane of the uterus in its 
non-placental area: dr, the mucous membrane reflected on to the placenta at its free border, 
—the shaded band to the left of the letters represents the line where the placental villi, 
through tearing down of the reflected decidua have been exposed; ch, the non-placental 
part of the chorion, Natural size. 
Pratt XIX. 
Figure 5. Vertical section through one lobule and a portion of an adjacent lobule of the placenta of 
the Grey Seal. Ch, chorion; VV, stems of the large arborescent villi; V’, smaller villi 
arising directly from the chorion. The blue-coloured vessels in the chorion and villi are 
the ramifications of the umbilical vein. 4g-.g., greyish membrane at the periphery of the 
lobule in which the blue-coloured vessels of the villi ramify; 0.0., bud-like offshoots of 
the finer branches of the villi; ds, uterine mucosa forming the non-deciduous serotina 
in relation with the placental lobules; g/, utricular gland; wv, uterine blood-vessels, 
coloured red, passing into /, a tertiary fissure between the two lobules. At the upper end 
of this fissure these vessels form a network continuous with the intra-lobular maternal 
capillaries. At ¢r the intra-placental trabecular arrangement of the mucosa is shown 
isolated and drawn away from the finer branches of the villi. In the greater part of this 
figure the maternal trabecule are shown in situ intertwined amidst the feetal villi. x 40. 
Figure 6. Uterine surface of four of the lobules of the placenta. g.g., greyish membrane forming the 
periphery of the lobules; at g’ the membrane has been dissected off; the blue-coloured 
vessels are branches of the umbilical vein; ¢, processes of the uterine mucosa, with the 
vessels coloured red, dipping into the tertiary fissures between the lobules. x 4. 
