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.)
56. The progressive increase of the Ovulum, from the time of its quitting the Ovarium until it has stationed itself firmly within the womb, has been demonstrated (Magendie, Prevost). In examining, between eight and twelve days after fecundation, the female organs of such of the mammalia as are multiparous at a single gestation, one Ovulum has been found near the fimbriated end of the fallopian tube of one size; a little farther into the tube another of a larger size; and lastly, near to the uterine orifice of the tube, a third of a still larger size; shewing the relative progressive increase that had taken place in such Ovula subsequently to a single act of fecundation, and proportionate to the time employed by such Ovula in travelling to the spot in which they were found. (Prevost, and Dumas’s 3rd Memoir on Generation.)
57. While thus circumstanced, the Ovulum is never connected with the part through which it passes. On plunging that part into water, the Ovulum is found not only to rise to the surface, but to float. (Home, Prevost, Dumas.)
58. What stronger proofs need be required of the existence of an inherent life-principle in the Ovulum, which is, at one time at least, (indeed I suspect throughout the period of gestation,) independent of any connection with the parent mother? (Plate I., and several of the explanations of figures throughout the work.) Yet none of the earlier writers who adopted the Ovarian theory of generation have ever asked themselves this question: What supports the vitality of a fecundated Ovulum after it has left the Ovarium, and previously to its becoming connected with the womb? In fact, the subject had never been mooted, before the more modern physiologists took it up and satisfactorily explained it[[8]].
59. That the embryo probably lives in utero in virtue of its own life-principle, even through the entire period of gestation, (51, 56, and 58,) is rendered probable by many facts related by unimpeached authorities, which go to prove that when the whole intact Ovum has been expelled at an advanced period of gestation, or at the natural termination of that period, the fœtus has continued to live, and the circulation of the blood has not ceased for an instant during a space of time of from nine minutes to a quarter of an hour. (Roederer, Wrisberg, Osiander, and Meckel, who repeated the experiments of the latter.) It has been asserted by a venerated authority that in an intact Ovum, expelled at seven months, the fœtus lived upwards of an hour. (Harvey.) The truth of this assertion is confirmed by very recent observers (Green, Velpeau, Gardien, Dr. Campbell)[[9]]. I once destroyed a female cat by prussic acid near the time of parturition; and having removed from the horns of the uterus the entire Ova, with their beautiful annular placentæ, while the fœtus in each of them was still perfectly lively, and could distinctly be seen, through the membranes, to move, I found that at the end of thirty-five, forty, and even forty-two minutes, some of them were still alive, the Ova remaining entire all the time, and upon the table[[10]].
60. When the Ovulum has made good its fastening to the adventitious lining of the womb (decidua), the circulation of the blood in it is as yet imperfect. The Ovulum does not—cannot—receive the blood of the mother. How could such a gossamer-like being, organized as the Ovulum has been proved to be, during the first days after fecundation, be made a part of so impetuous a torrent as the circulation of the blood of the mother, without instant destruction to the produce of conception? No. The blood of the embryo is first formed within itself. (Prevost, Home, Magendie, Adelon, Serres, Rolando.)
61. The newly-engendered being passes through two striking metamorphoses previously to the enjoyment of its extra-uterine life. These are the Embryonic and the Fœtal states. The latter succeeds immediately to the former; beginning at the moment when the new being is grafted on the maternal womb, and continuing until its expulsion from thence at the full period of gestation. It follows, therefore, that the Embryonic or former state is that in which the new being is as yet, without any direct or indirect communication with the mother, and still less so with external objects. This state persists for about two weeks after fecundation, during which the Embryo continues to derive its nourishment from the cortical membrane of the Ovum. (Boer, Soemmering, Plagge, myself.)
62. The growth and progress of the Embryo or Fœtus follow a very irregular march. Up to the second month the increase is somewhat slow—it is accelerated during the third—it slackens again at the fourth and fifth months—between which and the last month the increase is more rapid, until it has acquired its proper maturity. (Autenrieth, Soemmering.)[[11]]
63. The Embryo may be perceived, with the naked eye, at the fourteenth day after conception. It measures then 1–12th of an inch in length. (Dr. Pockels.) On the third week, it is 1–10th of an inch long. It is as large as a house-fly at four weeks, and as a horse-fly at six weeks. At two months it weighs twenty grains, and is one inch long. It weighs an ounce and a half at three months, and measures three inches; between which time and the sixth month it increases in dimensions from three to nine inches, and in weight from one ounce and a half to one pound. The relative weights of augmentation of length for the seventh, eighth, and ninth months stand thus:—from two to four pounds, and twelve inches; from four to five pounds, and seventeen inches: from five to eight pounds and twenty-two inches. (Averages of minute and accurate observations made by Autenrieth, Soemmering, Bichat, Pockels, Carus, &c.—confirmed by my own observations made on several early ova, and many fœtuses examined in the course of seventeen years obstetrical practice.)