PREGNANCY. 189 



muscle, imbedded in connective tissue and intermingled with 

 numerous large arterial and venous channels. The muscular 

 tissue is arranged in general in three strata, an inner and an 

 outer longitudinal and a middle circular layer ; but these 

 divisions are not very distinct and the arrangement is not very 

 definite. 



The outer surface of the uterus is covered with serous mem- 

 brane, consisting of the folds of the peritoneum reflected over 

 it. The bloodvessels of the uterus are unusually large, 

 abundant, and tortuous. 



The cervix of the uterus has a thicker mucosa, which is 

 thrown into rugae, and a more regular arrangement of the 

 three muscle-layers than the body of the organ. 



The upper portion of the cervical canal is covered with 

 simple ciliated epithelium ; but the loiter poiiion is lined with 

 stratified squamous epithelium, and the underlying tunica 

 propria presents numerous projecting papillae. 



In the lower part of the cervix mucous glands are present, 

 in addition to the uterine glands. From the closure of their 

 outlet-ducts these mucous glands often become distended with 

 secretion, forming small cysts called ovula of Naboth. The 

 outer surface of the cervix uteri is lined by the vaginal 

 mucous membrane. 



During menstruation the mucous lining of the uterus be- 

 comes much thickened ; the epithelium cells swell, the tunica 

 propria becomes very vascular and increases in thickness, and 

 the uterine glands enlarge. The mucosa becomes softened 

 and degenerated, and is finally cast off, mingled with blood, 

 as the menstrual discharge. After menstruation is over the 

 mucous membrane is rapidly renewed, the surface epithelium 

 being regenerated from the portions of the uterine glands 

 remaining in the depths of the tunica propria. 



During pregnancy there is a great hypertrophy or increased 

 development of the mucous and muscular coats and the vascu- 

 lar system of the uterus. The mucosa undergoes special 

 changes and to it become attached the placenta and foatal en- 

 velopes; it exhibits fusiform connective-tissue cells, large 

 numbers of decidual cells (large brown pigmented, round, or 

 polymorphous cells, sometimes multinucleated), dilated and 

 compressed lumina of the uterine glands, and an increase of 



