614: DEVELOPMENT OF UTERINE MUCOUS MEMBRANE. 



CHAPTER XI. 



DEVELOPMENT OF UTERINE MUCOUS MEMBRANE. 

 FORMATION OF THE DECIDUA. 



IN fish, reptiles, and birds, the egg is either provided with a sup- 

 ply of nutritious material contained within its membranes, or it is 

 so placed, after its discharge from the body of the parent, that it 

 can absorb these materials from without. Thus, in the egg of the 

 bird, the young embryo is supported upon the albuminous matter 

 deposited around the vitellus ; while in the frog and fish, moisture, 

 oxygen, saline substances, &c., are freely imbibed from the water 

 in which the egg is placed. 



But in the quadrupeds, as well as in the human species, the egg 

 is of minute size, and the quantity of nutritious matter which it 

 contains is sufficient to last only for a very short time. Moreover, 

 the development of the foetus takes place altogether within the body 

 of the female, and no supply, therefore, can be obtained directly 

 from the external media. In these instances, accordingly, the mu- 

 cous membrane of the uterus, which is found to be unusually 

 developed and increased in functional activity during the period of 

 gestation, becomes a source of nutrition for the fecundated egg. 

 The uterine mucous membrane, thus developed and hypertrophied, 

 is known by the name of the Decidua. 



It has received this name because, as we shall hereafter see, it 

 becomes exfoliated and thrown off, at the same time that the egg 

 itself is finally discharged. 



The mucous membrane of the body of the uterus, in the unimpreg- 

 nated condition, is quite thin and delicate, and presents a smooth 

 and slightly vascular internal surface. There is, moreover, no layer 

 of submucous cellular tissue between it and the muscular substance 

 of the uterus; so that the mucous membrane cannot here, as in 

 most other organs, be easily dissected up and separated from the 

 subjacent parts. The structure of the mucous membrane itself, 

 however, is sufficiently well marked and readily distinguishable 



