152 HUMAN PHYSIOLOGY. 



external, or peritoneal, (2) middle, or muscular, the fibres of which are 

 arranged in a circular or longitudinal direction, (3) internal, or mucous, 

 covered with ciliated epithelial cells, which are always waving from the 

 ovary toward the uterus. 



The Uterus is pyriform in shape, and may be divided into a body and 

 neck ; it measures about three inches in length and two inches in breadth 

 in the unimpregnated state. At the lower extremity of the neck is the os 

 externum ; at the junction of the neck with the body is a constriction, the 

 os internum. The cavity of the uterus is triangular in shape, the walls of 

 which are almost in contact. 



The walls of the uterus are made up of several layers of non-striated 

 muscular fibres, covered externally by peritoneum, and lined internally by 

 mucous membrane, containing numerous tubular glands, and covered by 

 ciliated epithelial cells. 



The Vagina is a membranous canal, from five to six inches in length, 

 situated between the rectum and bladder. It extends obliquely upward 

 from the surface, almost to the brim of the pelvis, and embraces at its upper 

 extremity the neck of the uterus. 



Discharge of the Ovum. As the Graafian vesicle matures, it increases 

 in size, from an augmentation of its liquid contents, and approaches the 

 surface of the ovary, where it forms a projection, measuring from one-fourth 

 to one-half an inch in size. The maturation of the vesicle occurs periodic- 

 ally, about every twenty-eight days, and is attended by the phenomena of 

 menstruation. During this period of active congestion of the reproductive 

 organs the Graafian vesicle ruptures, the ovum and liquid contents escape, 

 and are caught by the fimbriated extremity of the Fallopian tube, which has 

 adapted itself to the posterior surface of the ovary. The passage of the 

 ovum through the Fallopian tube into the uterus occupies from ten to four- 

 teen days, and is accomplished by muscular contraction and the action of 

 the ciliated epithelium. 



Menstruation is a periodical discharge of blood from the mucous mem- 

 brane of the uterus, due to a fatty degeneration of the small blood vessels. 

 Under the pressure of an increased amount of blood in the reproductive 

 organs, attending the process of ovulation, the blood vessels rupture, and a 

 hemorrhage takes place into the uterine cavity ; thence it passes into the 

 vagina. Menstruation lasts from five to six days, and the amount of blood 

 discharged averages about five ounces. 



Corpus Luteum. For some time anterior to the rupture of a Graafian 

 vesicle, it increases in size and becomes vascular ; its walls become thick- 



