234 HUMAN PHYSIOLOGY. 



forming the corona radiata. The nucleus consists of a nuclear mem- 

 brane enclosing material, some of which arranged in the form of thread 

 stains readily and hence known as chromatin in the meshes of which lies 

 a material and stains faintly and hence known as achromatin. 



The Fallopian tubes are about four inches in length, and extend outward 

 from the upper angles of the uterus, between the folds of the broad ligaments, 

 and terminate in a fringed extremity which is attached by one of the fringes 

 to the ovary. They consist of three coats: 



1. The external, or peritoneal. 



2. Middle, or muscular, the fibers of which are arranged in a circular and 

 longitudinal direction. 



3. Internal, or mucous, usually folded longitudinally is 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 ex- 

 tern um; 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 the 

 triangle being almost in contact. 



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

 fibers, 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 ex- 

 tremity 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 to i 

 of an inch. The maturation of the vesicle occurs periodically, 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 fourteen days, and is 

 accomplished by muscular contraction and by the action of the ciliated 

 epithelium. 



