Lectures on the comparative anatomy of the placenta : first series : delivered before the Royal college of surgeons of England, June, 1875 /

Abstract

From the margin of the area germinitiva a delicate fold arises, which, by becoming more and more elevated, gradually extends itself above the back of the young embryo, until at last the folds from opposite sides meet in the middle line, become continuous with each other, and form the membrane of the amnion. Between the amnion and the back of the embryo is a space, the cavity of the amnion, which increases in size by, the secretion of the liquor amnii into it. The amnion consists of two layers, an outer and an inner, and as it is derived from the area germinitiva it is necessarily continuous with the blastoderm. The inner layer of the amnion, which lies next the amniotic cavity, consists of tessellated epithelial cells, is derived from the epiblast, and is continuous with the cuticular layer of the embryo. The outer layer of the amnion 9 9 * .;

Sir William Turner and his studies on the mammalian placenta

“…In 1875 and 1876, he gave a series of lectures to the Royal College of Surgeons of England on its structure and comparative anatomy. The substance of the first series of lectures was published in The Journal of Anatomy and Physiology in 1876 3 and the full account was published as a book in 1876 4 . Turner's comment at the beginning of the former article was that the observations formed the conclusion of his second series of lectures.…”

“…They had not only lost their tubal cylindrical form but had become expanded into a freely communicating series of irregular cavernous intraplacental sinuses. Therefore their derivation from the vessels of the non‐gravid mucosa was at first sight, difficult to recognize 4 …”

“…For example, he wondered whether some nutritive gain was achieved by the modifications of arrangement of the villi, which were concentrated in a zone or disc, rather than when diffused over an extensive surface. He suggested that dilated ­capillaries or sinuses may have caused less friction to blood flow than an ordinary capillary plexus 4 …”

“…An example of this might be lemurs, which have a diffuse placenta, in contrast to monkeys, which have a discoid placenta. He concluded ‘that for the purposes of classification, the placenta cannot be accepted as a dominant organ; but that in the present state of science, where our acquaintance with the genealogical relations of animals is insuf­ficient for the construction of a definite pedigree, the presence of a definite combination of similar characters drawn from more than one system of organs gives a safer guide to the affinities of an animal, than the existence, in only a single organ or system, of even a very close resemblance in form and structure’ 4 …”