23. The existence of the cortical membrane is proved in many parts of the present work, but particularly by Fig. 15, Plate III., and Fig. 17, Plate IV. in both of which specimens of abortion, the said _cortex_ had persisted to a longer period than usual during gestation, and had become, consequently, thickened, opaque, fleshy indeed, and the cause of abortion. Figure 15, too, shews strongly the probability of my notion that the thin membrane investing the surface of the yellow body of the ovulum is, in good truth, what has been usually denominated the shaggy chorion. 24. Another proof, amounting to demonstration, of the existence of a cortical covering to the human ovulum, and that of the filiform envelope called the shaggy chorion within it, I find in a striking and beautiful preparation belonging to Sir Charles Clarke, marked 87. We there see a complete cast of the lining (caducous membrane) of the uterine cavity after fecundation, thrown off at a very early period, and with it the ovulum, (of the size of a Portugal grape,) exhibiting the _cortex ovi_, shelly and membranaceous, of a dense texture, yet flexible, which has burst like the pericardium of some seeds, and allows the shaggy chorion beneath it to be seen. It is a curious fact, that even Ruysch has, in his fanciful manner, represented a human ovulum of about three weeks with the cortex burst, yet still _in situ_, and the shaggy chorion beneath it, in every way resembling the specimen of Sir Charles Clarke’s in the Museum of St. George’s Hospital. 25. Even the errors of some of the very able anatomists of the present day come in beautifully to corroborate Professor Boer’s observations of the cortical membrane. Breschet and Velpeau, for instance, state, that within what they (with their predecessors) have looked upon as the decidua in the human ovum, there is a cavity containing a peculiar liquid which, in their opinion, is essential to the nutrition of the fœtus. Now what is this but the very description of the ovulum by Boer (17), proving that there is a cortical membrane in the human ovum? 26. The cortical membrane is destined to be absorbed during the first months of utero-gestation, thus exposing the next membrane to the contact of the uterine lining (decidua), with which a connection takes place in that part where the placenta is to be formed. In that part, however, the cortex ovi is never altogether obliterated, but only made thinner; and, in process of time, it is converted into a mere pellicular envelope, which not only serves to divide the filiform vessels of the chorion into groups or cotyledons in order to form the placenta, but also covers all over those cotyledons or groups of vessels. (Plate I. Expl. of Fig. 1.) I have called this the _membrana propria_[2].