254 MICROSCOPIC ANATOMY OF THE ORGANS. 



lare), and an outer layer which consists exclusively of longi- 

 tudinally disposed elements (stratum subserowm). The middle 

 layer or stratum vasculare is by far the thickest of these coats. 



The serosa is not different in structure from other parts 

 of the peritoneum. 



The arteries enter the rnuscularis and divide mainly in 

 the stratum vasculare into numerous branches, of which the 

 greater part run into the mucosa and break up there into 

 capillary networks which surround the glands and reach up to 

 the, surface epithelium. The veins form a plexus in the deeper 

 parts of the mucosa, and then pass into the stratum vasculare, 

 where another larger plexus is formed. 



The lymph-vessels form a network in the mucosa and 

 another under the serosa. These are joined by anastomosing 

 branches. 



The nerves end partly in the muscularis (see Nerve-end- 

 ings), and partly in the mucosa, where they form thick net- 

 works. From these, non-medullated fibres run, according to 

 some authors, to the epithelium, where they end freely between 

 the cells. Ganglion cells have been described in the course of 

 these fibres. 



In certain phases in the life of the uterus changes take 

 place especially in the mucosa which must be spoken of here. 

 These changes accompany menstruation and pregnancy. 



In menstruation there is a certain amount of bleeding from 

 the uterus occurring more or less regularly every twenty-eight 

 days, and continuing throughout the life of the individual from 

 the fourteenth to about the forty-fifth or fiftieth year. It is 

 probable that the changes in the mucosa have to do with the 

 reception and preservation of the ovum, since ovulation occurs 

 at about the same time as menstruation. During the menstrual 

 period, in the first place, there is a marked hypersemia of the 

 uterine walls five to ten days before the flow of blood. The 

 blood-vessels are much dilated and the capillaries become large 

 and well marked. According to Heape, there is also an 

 increase in the number of blood-vessels. On account of the 

 hypersemia there are a swelling and a growth of the mucosa, 



