43. On the cortex bursting, the lanuginous or fibrillous membrane within it (21) is exposed, when the fibrils will forthwith entwine themselves with the flocculi of the decidua, and thus the Ovulum fastens itself to the uterus by one or more contiguous points. (Carus.) 44. The membrane having these fibrils on its surface, has been called the Chorion—and from the circumstance that these fibrils, both before the cortex which lies over them has burst, as well as afterwards, serve to promote the nourishment of the fœtus, I have styled it, the nutritive membrane or involucrum of the fœtus. It has been so considered by Ruysch, who calls the villous side of the Chorion, “_succosa nutritioni fœtus inserviens_.” 45. The fibrils of the Chorion have generally been considered as filiform vessels. When examined with the microscope, they appear diaphanous and ramiform; some of them terminate into little bulbs like the ampullæ of the villosities of the intestines. These bulbs adhere so firmly to the cortex ovi, that when an attempt is made to detach them, many are lacerated. (Carus.) It is only when the cortex bursts of its own accord that they are set at liberty. (43.) 46. These fibrils, however, are not all vessels. Some are only suckers, others are real vessels. (Carus.) The existence of any vessels among the fibrils of the Chorion has been denied very recently upon the same ground, namely, microscopical observations. (Breschet and Raspail.) But there must be an evident mistake in such observations; for the actual progress of those filiform vessels, and their gradual swelling into large veins and arteries, at an advanced period of fœtation, have been noticed in examining various human ova of different ages. (Lobstein, Velpeau, Dutrochet, and myself.) 47. The nutritive envelope or involucrum, or membrane (Chorion) of the Ovum is bifoliated. I have a beautiful preparation of the transparent membranes of the Ovum, even after regular parturition, which proves this fact. It is probably even trifoliated. (Dutrochet.) A fluid has been found between the two laminæ of the Chorion. (Meckel.) 48. The internal surface of the Chorion is likewise supplied with fibrils, which connect it with the next and innermost involucrum of the fœtus, called the Amnion. Between the fibrils or filiform vessels of the two surfaces, a communication is kept up by small vascular trunks which meander between the two laminæ of the Chorion. (Meckel and myself.) 49. The vascularity of the Chorion is further proved by its diseases, chiefly of an inflammatory character, ending in the thickening of its texture. (Plate III., page 12—Plate IV., page 13—Plate V., page 17—and many other examples in this Work.) There is a preparation in Sir Charles Clarke’s collection which shews the vessels of the Chorion as evidently as if they were injected.