THE FCETAL MEMBRANES OF MAN. 253 



ordinary abundance of cells, some of which are spindle-shaped, others 

 roundish. 



From the beginning of pregnancy the mucous membrane undergoes 

 very profound changes, which affect all parts. Concerning these we 

 possess accurate observations, which relate to every month of preg- 

 nancy, by KUNDRAT UND ENGELMANN, as well as by LEOPOLD and 

 SEDGWICK MINOT. 



We take up in succession (1) the decidua vera, (2) the decidua 

 reflexa, and (3) the decidua serotina or placentalis, the part which 

 enters into the formation of the placenta. 



(1) Decidua vera. As LEOPOLD remarks, with the beginning of 

 pregnancy the mucous membrane constantly increases in thickness, 

 until it becomes 1 cm. or more thick, up to the time, indeed, when 

 the growing ovum attaches itself completely to the walls of the 

 uterus, therefore approximately up to the end of the fifth month. 

 From that time forward there begins, as it were, a second stage, in 

 which, under the pressure of the growing foetus, it again becomes 

 thin and finally is only 1 to 2 mm. thick. Meanwhile both the 

 glands and the tissue between them undergo changes. 



During the first stage the uterine glands, which at the beginning 

 are tubes of uniform calibre, increase in size, especially in their 

 middle and deeper parts (fig. 146) ; whereas at their open ends 

 they are rectilinear and drawn out lengthwise, deeper down 

 they take a spiral course and are covered with evaginations and 

 pocketings. 



Upon sections therefore one can now distinguish two layers in the 

 decidua vera : 



(1) An outer more compact layer (G), possessing more abundant 

 cells, and 



(2) A deeper ampullar or spongy layer (Sp). 



In the former one sees the glands as elongated, parallel canals. 

 In consequence of a great growth of the inter-tubular tissue they 

 are separated from one another farther than at first ; they begin at 

 the surface with enlarged funnel-shaped pits (tr). The surface of a 

 mucous membrane stripped off from the musculature has, as KOLLIKER 

 states, a sieve-like appearance, due to the enlarged orifices of the glands. 



In the spongy layer (Sp) one encounters irregular, lobed 

 cavities (dh) one above another, the capacity of which continually 

 increases up to the middle of pregnancy, and which are finally 

 separated from one another by thin septa and cords of the matrix- 

 tissue only. The appearance is explained by the fact that in the 



