MENSTRUATION AND OVULATION. 651 



lary blood vessels, the tunica vasculosa, and to these two coats 

 collectively the terra tunica propria is applied. 



Inside the tunica propria are granular cells of small size, 

 which occupy a considerable space in the follicle; they are heaped 

 up at one spot to receive the ovum, which lies imbedded in their 

 midst. These cells receive the name of the tunica granulosa, and 

 their projecting portion, which encircles the ovum, is called the 

 discus proligerus. Filling up the remainder of the follicle is a 

 fluid the liquor folliculi. The surface of the ovary is covered by 

 columnar cells, which are continuous with the endothelial cells 

 of the peritoneum. When the follicle is fully matured, it lies at 

 the periphery of the ovary beneath this layer of cells, which 

 separates it from the abdominal cavity. 



MENSTRUATION AND OVULATION. 



After puberty, at intervals averaging about four weeks, the 

 genital organs of the female become congested, and at the same 

 time a Graafian follicle is ruptured and its contained ovum set 

 free. Coincidently with the rupture of the follicle, the fimbriated 

 extremity of the Fallopian tube becomes closely approximated 

 to the spot where the follicle lies, so that the ovum, instead of 

 falling into the abdominal cavity, passes into the canal of the 

 Fallopian tube, down which it is conveyed to the uterus. 



The usual place for the ovum to meet the spermatozoa, and to 

 be impregnated, is the Fallopian tube. 



When the ovum reaches the uterus, if it be unimpregnated, it 

 is cast out with the surface cells of the mucous membrane of the 

 uterus, which are destroyed, and escape along with a sanious fluid. 

 The whole of the phenomena constitute a menstrual act. 



If, however, the ovum become impregnated, it remains in the 

 Fallopian tubes some days, during which time the mucous mem- 

 brane of the uterus becomes so hypertrophied and developed as 

 to retain the ovum when it reaches that organ. 



The human ovum is a cell consisting of a mass of protoplasm 

 inclosing a nucleus and a nucleolus, and surrounded by a cell 

 wall. On its outer surface is an irregular layer of cells, the 

 remains of that part of the tunica granulosa which encircled the 



