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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



found than those. The supply of blood to the walls is greatly increased, the 

 vessels forming large irregular sinuses within the mucosa. The supply of lymph 

 is increased. The glands become tortuous and dilated into flattened cavernous 

 spaces, and their walls atrophy, the epithelium breaking down except in their 

 deepest parts. The mucosa is thus converted into a spongy tissue, the frame- 

 work of which contains numerous large irregular cells, derived probably from 

 the original connective tissue and called decidual cells. The musculature is 



Decidua serotina. 

 Ckorion frondosum. 



Muscle. 



Uterine glands. 

 Chorion Iseve. 



Mucous plug within cervical canal. 



FIG. 314. Diagram of the human uterus at the seventh or eighth week of pregnancy (modified from 

 Allen Thompson). The fetal villi are shown growing into the sinuses of the decidua serotina and the 

 decidua reflexa ; in the latter they are becoming atrophied. They are marked by the black fetal vessels, 

 which can be traced backward along the umbilical cord to the embryo. The placenta comprises the 

 decidua serotina and the chorion frondosum. 



greatly thickened by an increase, partly in number and partly in size, of its 

 constituent fibres, and the nerve-supply is increased. These general structural 

 changes proceed through the early part of gestation and are accompanied by 

 special changes to be discussed later. It is not definitely known how far the 

 alterations have gone before the advent of the segmented ovum in the uterus. 



