50. But the vascularity of the transparent membranes is proved further by fine injections thrown into the vessels of the ovaria of women; on which occasion a beautiful net-work of minute vessels is rendered manifest, forming a species of vascular ring around the _Vesiculæ Graafianæ_. The same observation has been made by comparative anatomists. (Cuvier, Home, Lobstein.) 51. These facts, demonstrative and corroborative of the vascularity of the Chorion, (45, 46, 48, 49,) explain and account for the reality of that self-existing life-principle inherent in the fecundated Ovum (42), which detaches it from its nest (vesicula Graafiana), enables it to travel through the tube, to grow or expand while thus travelling, and to maintain that same power of growth and development for a short time after its reception into the womb, until its final and effectual implantation on the maternal stock (uterus). 52. The same holds good with regard to the amnion, or inner transparent membrane of the Ovum, which, although normal anatomy has failed, morbid anatomy has succeeded in proving to be vascular. (Plate VI. fig. 20, and Description, p. 19, and Remarks, pp. 20–24.) (Haller, Monro, Chaussier, Meckel.) 53. If it be true that the amnion is a vascular membrane, there is no difficulty in viewing it also as a secreting membrane. Hence the source of that particular fluid, to which the name of Liquor Amnii has been given, and in which the embryo is suspended to the end of gestation. (Plate I. fig. 4, but particularly fig. 7, 8, and 9, and Remarks.) 54. The amnion is a sac formed by the reflected epidermis of the embryo. (Velpeau, Boer, Pockels.) It does not exist before the twelfth day. (Velpeau.) At the eighteenth day it is found as a bladder placed on the back of the embryo, and continuous to it along its edges or sides and at its extremities. (Velpeau.) It has been distinctly seen on the twelfth day. (Pockels.) It is then not a concentric membrane within the chorion, but a vesicle, on the outside of which the embryo rests as on a bed. Until the day in question the embryo is connected to the vesicular amnion at the back, by a cellular transparent membrane. From that time till the sixteenth day the embryo progressively gets into the cavity of the amnion, which before was connected with the chorion by one of its piriform extremities, while the other conical extremity penetrates slowly into the albuminous fluid of the chorion. (Pockels.) 55. While the embryo is within the chorion (nutritive involucrum) and rests on the vesicular amnion, the former membrane, or sac, contains a reddish transparent fluid having the consistency of the albumen of an egg, (54.) with a colourless and very slender membrane crossing it in various directions. (Pockels.)