THE DECIDUA VERA. 



47 



the tubular depressions ; the inner portions of the glands, directed towards the sur- 

 face of the uterus, become elongated and lie embedded within a comparatively 

 dense matrix. In consequence of these changes, the decidua in the vicinity of the 

 ovum, where the hypertrophy is most marked, presents in section two strata, an 

 inner cojupad and an outer spongy layer. The ciliated columnar epithelium that 

 normally clothes the free surface of the uterus, and perhaps also the uterine glands, 

 gradually disappears, the degeneration beginning before the end of the first month. 

 The integrity of the cells lining the uterine glands is maintained for a longer period, 

 but the glandular epithelium likewise, after a time, suffers, losing its columnar 

 character and changing to small cubical or flattened elements, which, after appear- 

 ing as shrunken columns during the fourth and fifth months, finally disappear 

 during the latter half of gestation. An important exception, however, is to be noted 

 in the behavior of the epithelium lining the deeper portion, or the fundus, of the 

 glands next the muscular tissue ; the epithelium situated in this position does not 

 participate in the atrophic changes above described, but retains more or less per- 



FiG. 54. 



Free surface 



Enlarged gland 



Blood-vessel 



Enlarged gland 



Uterine muscle 



Section of mucous membrane lining body of uterus (decidua vera) ; fourth month of pregnancy. {After Leopold.') 



fectly its normal condition to the close of pregnancy. After the expulsion of the 

 decidual portion of the uterine mucous membrane, the epithelium remaining in the 

 fundus of the glands becomes the centre of regeneration for the new lining of the 

 uterus. 



The connective-tissue elements of the matrix surrounding the glands, especially 

 in the compact layer in the vicinity of the ovum, undergo active proliferation, in 

 consequence of which large spherical elements, the decidual cells, are produced. The 

 latter, from .030 to .040 millimetre in diameter, in places are so densely packed 

 that they assume the appearance of epithelium ; although most tvpical and nu- 

 merous in the compact layer, they are, nevertheless, present in the spongy stratum, 

 in this situation being more elongated and lanceolate in form. 



The decidua vera retains this general character during the first half of preg- 

 nancy ; from this time on, however, the increasing volume of the uterine contents 

 subjects the decidua to undue pressure, in consequence of which the hypertrophied 

 mucosa undergoes the atrophic changes characteristic of the so-called second stage. 

 These include a gradual reduction in the thickness of the decidua vera from nearly 



