972 OF GENERATION. 



the membrane into a number of villous prolongations, at first composed entirely 

 of cells, which give it a spongy or shaggy appearance (Plate I. Fig. 10). These 

 serve as absorbing radicles, and form the channel through which the embryo is 

 nourished by the fluids of the parent, until a more perfect communication is 

 formed, in the manner to be presently explained. 



977. We have now to speak of the changes in the Uterus which take place 

 in consequence of Conception, and which prepare it to receive the ovum. Of 

 these the most important is the formation of the Membrana Decidua, so called 

 from its being cast off at each parturition. This membrane has been usually sup- 

 posed to be a new formation ; and has been described as originating in coagulable 

 lymph thrown out on the inner surface of the uterus, into which vessels are pro- 

 longed from the subjacent surface. It appears, however, from the researches of Dr. 

 Sharpey and Prof. Weber, 1 that this is not the true account of it ; and that the 

 Decidua vera is really composed of the inner portion of the Mucous membrane 

 itself, which undergoes a considerable change in its character. The Mucous mem- 

 brane of the uterus possesses on its free surface a tubular structure (Figs. 248, 

 249) ; not very unlike that which has been described as existing in the lining 

 membrane of the stomach ( 440). This tubular portion becomes thickened 

 and increased in vascularity, within a short time after conception ; and when 

 the inner surface of a newly-impregnated uterus is examined with a low mag- 

 nifying power, the orifices of its tubes are very distinctly seen, being lined with 

 a white epithelium. The bloodvessels form a very minute network, which ex- 

 tends in loops from the subjacent portion of the membrane. According to the 

 observations of Prof. Groodsir, 3 the interfollicular spaces also are crowded with 

 nucleated particles ; and it is to the development of this interfollicular sub- 

 stance, as well as to the enlargement of the follicles themselves, and the copious 

 development of epithelial cells in their interior, that the mucous membrane in 

 this condition owes its increased thickness. This increased development appears 

 to have reference in part to the temporary nutrition of the ovum, and in part 

 to the further evolution of the decidual substance itself in the formation of the 



Fig. 248. 



Section of the lining membrane of a Human Uterus at the period of commencing pregnancy, showing the 

 arrangement and other peculiarities of the glands d, d, d, with their orifices a, a, a, on the internal surface 

 of the organ. Twice the natural size. After E. H. Weber. 



Placenta. The cavity of the uterus shortly becomes filled with a fluid, evidently 

 poured out from the follicles in its walls, and containing a large number of 

 nucleated cells ; and in this the villi of the chorion are imbedded, obviously 

 for the purpose of deriving from it the materials required for the development 

 of the embryonic structures. These villi are easily traced in the bitch (as Dr. 

 Sharpey first pointed out) into the mouths of the uterine glandulae, some of 

 which are composite in their structure, a single outlet being common to a num- 

 ber of follicles; but they have not yet been so traced in the Human subject. 



1 Muller's "Elements of Physiology," pp. 1574-1580. 



2 "Anatomical and Physiological Observations," chap. ix. 



