FORMATION OF 7HE DECIDUA. 



903 



growth of the margin of the cup over the free surface of the ovum, closes 

 iu the chamber and forms the membrana decidua reflexa 1 (Fig. 318), by 

 which the ovum is entirely covered about the twelfth or thirteenth day. At 



FIG. 318. 



'<!'< ;ifv^ 



First stage of the formation of the Decidua 

 reflexa around the ovum. 



More advanced Stage of Decidua reflexa. 



FIG. 310. 



the margin of the cotyledonary island, the uterine mucous membrane is 

 smooth, and shows the widened orifices of the uterine glands. Some utric- 

 ular glands are also found opening on the inner concave surface of the 

 reflexa, the rest of the surface being covered with a short, non-ciliated 

 cylindrical epithelium. As the ovum increases in size, the cavity between 

 the decidua vera and the decidua reflexa, or, as it is sometimes termed, the 

 uterine chamber, gradually diminishes, and by the end of the third month 

 either the two layers come into contact and are henceforth indistinguishable 

 the whole cavity of the uterus being occupied by the foetal chamber or, 

 as Dr. Farre suggests, the decidua reflexa may, after first becoming extremely 

 attenuated, ultimately entirely vanish. 



753. The surface of the Ovum, thus surrounded by the double layer of 

 the deciduous membrane, and during the 

 first three or four weeks lying loose in the 

 foetal chamber, is rendered shaggy by the 

 growth of villous tufts from the surface of its 

 investing Chorion (Fig. 319), by which it be- 

 gins to be attached to the walls that surround 

 it. Each of these tufts, as was first pointed out 

 by Prof. Goodsir (loc. cit.), is composed of 

 an assemblage of nucleated cells, which are 

 found iu various stages of development ; 

 and these are always inclosed within a layer 

 of basement-membrane, which seems to be 

 itself composed of flattened cells united by 

 their edges. At the free extremity of each 

 villus is a bulbous expansion, the cells com- 

 posing which are arranged round a central 

 spot ; and it is at this point that the most 

 active processes of growth take place, the 

 villus elongating by the development of new 



Cells from its germinal Spot, and (like the Entire Human Ovum of eighth week, 



Spongiole Of the plant) drawing iu niltri- sixteen linos in length (not reckoning the 



P,. , ., . , . i ., i ji i tufts); the surface of the Chorion partly 



ment from the soil in which it is imbedded. sraoothj aml partly rendered shaK ,, v ,, v 

 In its earliest grade of development, the the growth of tufts. 



1 See Turner's Keport, Journal of Anatomy and Physiology, vol. viii, p. 



