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ESSENTIALS OF PHYSIOLOGY. 



a fatty pigment, lutein. It gradually undergoes fibrous changes and 

 disappears within two months. If pregnancy occurs, the corpus luteum 

 becomes much larger and does not disappear until after parturition. 

 The primordial ova are extremely numerous in the ovary, but only a 

 small proportion of them develop into Graafian follicles, and only a few 

 of the latter reach maturity and burst, the others, after developing to 

 a certain extent, undergoing atrophy. During sexual life ovulation 

 usually occurs once a month, a single ovum being discharged on each 

 occasion. The process is intimately bound up with menstruation. 



The Uterus. The uterus consists of two parts, the body and the 

 cervix. Its cavity is lined by a thick mucous membrane, composed of 

 soft connective tissue covered by ciliated epithelium which dips down 

 into the membrane to form long tubular glands. 



The mucous membrane rests on a thick muscular coat arranged in 

 two layers. The fibres of the outer layer run chiefly longitudinally, 

 but some run circularly ; the fibres of the inner layer, which is much 

 thicker than the outer one, run circularly, and are really a greatly 

 hypertrophied muscularis mucosse. 



The Fallopian (uterine) tube consists of a mucous membrane thrown 

 into numerous longitudinal folds and lined by ciliated epithelium. 

 The mucous membrane rests upon a muscular coat, the outer fibres 

 being longitudinal and the inner circular. 



Both the uterus and Fallopian tubes are covered by a serous 

 membrane derived from the peritoneum. 



Menstruation. This marks the onset of puberty, and occurs first 

 between the ages of 1 3 and 16; as a rule, it recurs once a month until 

 about the age of 45, its cessation at this age being called the menopause. 



Each month the mucous membrane of the uterus becomes con- 

 gested and thickened, and eventually some of the blood-vessels of the 

 membrane rupture ; the escaping blood, together with the superficial 

 epithelium of the uterus and the secretion of the uterine glands, form 

 the menstrual flow, which lasts four or five days, the loss of blood 

 varying from 100 to 300 c.c. When it ceases, the mucous membrane 

 of the uterus is gradually regenerated, and returns to its original 

 condition. 



Menstruation is associated with feelings of malaise and often with a 

 slight rise of temperature. It is absent during pregnancy, and usually 

 during lactation, and is undoubtedly related to and dependent upon 

 ovulation, though the latter may either precede or follow the menstrual 

 flow. Menstruation ceases after the removal of the ovaries, and also 

 at the menopause, when ovulation no longer takes place ; its object 

 appears to be to render the condition of the uterus, at the end of the 



