(JKXK RATION AND DEVELOPMENT. 



267 



The glands are lined by columnar ciliated epithelium, and they open 

 on the inner surface of the mucous membrane by small round orifices set 

 closely together (a, a, Fig. 420). 



On the internal surface of the mucous membrane may be seen the cir- 

 cular orifices of the glands, many of which are, in the early period of 

 pregnancy, surrounded by a whitish ring, formed of the epithelium which 

 lines the follicles (Fig. 426). 



Membrana decidua. Coincidently with the occurrence of preg- 

 nancy, important changes occur in the structure of the mucous membrane 



FIG. 427. Diagrammatic view of a vertical transverse section of the uterus at the seventh or 

 eighth week of pregnancy, c, c, c', cavity of uterus, which becomes the cavity of the decidua, open- 

 ing at c, c, the cornua, into the Fallopian tubes, and at c' into the cavity of the cervix, which is 

 closed by a plug of mucus: d v, decidua vera; d r, decidua reflexa, with the sparser villi imbedded in 

 its substance ; d s, decidua serotina, involving the more developed chorionic villi of the commencing 

 placenta. The foetus is seen lying in the amniotic sac; passing up from the umbilicus is seen the 

 umbilical cord and its vessels/passing to their distribution in the villi of the chorion ; also the pedicle 

 of the yelk-sac, which lies in the cavity between the amnion and chorion. (Allen Thomson.) 



of the uterus. The epithelium and sub-epithelial connective tissue, to- 

 gether with the tubular glands, increase rapidly, and there is a greatly 

 increased vascularity of the whole mucous membrane, the vessels of the 

 mucous membrane becoming larger and more numerous; while a sub- 

 stance composed chiefly of nucleated cells fills up the interfollicular spaces 

 in which the blood-vessels are contained. The effect of these changes is 

 an increased thickness, softness, and vascularity of the mucous mem- 

 brane, the superficial part of which itself forms the memlrana decidua. 



