Chap. XXI] THE ORGANS OF GENERATION 453 



gestion of the generative organs, including the breasts, accom- 

 panied by more or less discomfort and even pain. The mucous 

 membrane of the uterus undergoes the following changes : (1) there 

 is marked hypertrophy and congestion of the mucous membrane, 

 (2) during menstruation there is capillary hemorrhage and the 

 epithelium of the mucous membrane is cast off, (3) following 

 menstruation a new epithelium is formed and the mucous mem- 

 brane returns to its normal size. 



Comiection between ovulation and menstruation. — Whether 

 ovulation depends upon menstruation or menstruation upon 

 ovulation, or whether either has any connection with the other, 

 is a matter of lengthy controversy. At the present time the 

 generally accepted view is that menstruation is dependent upon 

 the ovaries, and that their influence is exerted through the medium 

 of the blood. It is thought that an internal secretion is formed in 

 the ovaries, possibly by the corpus luteum. This secretion is 

 carried to the uterus by the blood and is responsible for the hyper- 

 trophy and congestion that precedes menstruation. So far it has 

 not been possible to decide whether the internal secretion is en- 

 tirely responsible for menstruation, or whether it is partly due to 

 a power inherent in the uterine muscle. The fact that operations 

 for the removal of the ovaries are followed by atrophy of the uterus 

 and cessation of menstruation, supports the theory that the ovaries 

 are responsible for menstruation. 



Purpose of menstruation. — The purpose of the hypertrophy 

 and congestion of the uterus is thought to be nature's way of 

 preparing the uterine walls for the reception of the ovum should 

 it become fertilized. 



Mammary glands. — The two mammary glands, or breasts, 

 may be considered as accessory organs of generation. 



Function. — The function of the mammary glands is to 

 secrete the milk which is needed for the nourishment of the 

 young infant. 



Location. — Each breast covers a nearly circular space in front 

 of the pectoral muscles, extending from the second to the sixth 

 rib, and from the sternum to the border of the arm-pit. 



Structure. — The breasts are covered externally by skin, are 

 convex in shape, and about the centre of the convexity a papilla 

 projects, which is called the nipple. The nipple contains the 



