UTERUS 363 



late pregnancy is an unsolved problem, similar to that presented by the 

 musculature of the bladder and intestine during distention. 



The serosa covering the dorsal and ventral surfaces of the uterus is in 

 part a well-defined layer, but it blends with the connective tissue of the 

 broad ligaments laterally and below; and this tissue, from its position 

 beside the uterus, is known as the "parametrium." Imbedded in the 

 parametrium the main trunks of the uterine vessels run along the lateral 

 margins of cervix and corpus, both artery and vein showing many kinks 

 and convolutions. The vessels are thus apparently adapted to the future 

 expansion of the uterus, but when it retracts after pregnancy they are 

 said to show more pronounced bendings, as if they had been permanently 

 elongated. The parametrium contains also numerous lymphatic vessels, 

 together with the ganglionated sympathetic utero-vaginal plexus. Nerves 

 from this plexus and from the third and fourth sacral nerves supply the 

 uterus. 



MENSTRUATION. 



Menstruation is the periodic degeneration and removal of the super- 

 ficial part of the mucosa of the uterus, accompanied by haemorrhage from 

 the vessels of the tunica propria. Three successive stages may be dis- 

 tinguished, namely (i) the stage of congestion, lasting four to five days; (2) 

 the stage of desquamation and hamorrhage, four days; and (3) the stage of 

 regeneration and repair, seven days. Thus the entire process requires 

 about sixteen days, and after an interval of twelve days the cycle begins 

 anew. 



For four or five days before the discharge occurs, the thickness of the 

 mucosa increases greatly, due to the congestion of its vessels and the 

 proliferation of the reticular tissue. The glands become wider, longer, and 

 more tortuous, opening between irregular swellings of the superficial 

 epithelium. Red corpuscles pass out between the endothelial cells of the 

 distended veins and capillaries, and form subepithelial masses. This 

 stage of congestion and tumefaction is followed by one of haemorrhage and 

 desquamation. The epithelium of the surface and outermost parts of the 

 glands becomes reduced to granular debris, or it may be detached in shreds. 

 The underlying vessels rupture and add to the blood which had escaped by 

 diapedesis. In the stage of regeneration, the epithelium spreads from the 

 glands over the exposed reticular tissue, the congestion diminishes, and 

 the mucosa returns to its resting condition. The cervix takes no part in 

 menstruation except that the secretion of its glands may increase during 

 the stage of congestion. 



Beginning at puberty (13-15 years) menstruation takes place normally 

 once in 28 days for 33 years, more or less. During pregnancy it is interrupted, 



