260 The Vertebrate Organ Systems 



The Ovaries. — The mamalian ovaries are somewhat flattened, bean- 

 shaped organs located in the abdominal cavity slightly posterior to the 

 kidneys. They are quite small in human beings, measuring only one 

 and one-half inches in length by about three-fourths inches in width. 

 Each ovary is attached to the broad ligament of the uterus by means of a 

 mesentery, the mcsovarimn. 



Histologically, the ovary, (Fig. 7B>) is seen to consist of a matrix of 

 connective tissue covered with a germinal epithelium. It is this epithe- 

 lium that gives rise to the female germ cells and follicles in the embryo. 

 In the newborn infant there are approximately 400,000 follicles, but 

 during the lifetime of the individual, no more than 400 mature to dis- 

 charge their ova. The remaining ones gradually disintegrate and dis- 

 appear and possibly may function to produce the female sex hormones. 



ruuy FOAMED 

 CORPUS LUTEUU 



DOUBLE LAYERED 

 FOLLICLE 



MATURE FOLLKUJE 



GERMINAL 

 EPITHELIUM 



Fig. 78. — A semidiagrammatic section of the ovary. 



During the reproductive life of the individual, single follicles grad- 

 ually sink into the matrix of the ovary and enlarge. During this period, 

 the ovum gradually increases in size and the number of follicular cells 

 becomes greater. The follicle fills with fluid and gradually bulges from 

 the surface of the ovary. It is known as a Graafian follicle. Ovulation 

 occurs when the follicle ruptures to discharge the ovum into the oviduct. 

 After ovulation, the follicular cells change and contain a yellow pig- 

 ment; this body is the corpus luteum. If the ovum is not fertilized, 

 this body gradually disintegrates. 



The Reproductive Tract.— The female genital tract (Fig. 77) is 

 formed of the oviducts or fallopian tubes, the uterus, and the vagina. In 



