768 



A TEXTBOOK OF PHYSIOLOGY 



multiply, and a fluid becomes secreted between them, so that a mature 

 follicle is formed, the outer layer of cells forming what is known as 

 the membrana granulosa, which is enclosed in a fibrous capsule derived 

 from the stroma, and an inner ovum surrounded by a mass of cells, 

 known as the discus proligerus, the remainder of the follicle being 

 filled with fluid, the liquor folliculi. When fully mature, the follicle 

 is of such a size that it bulges the surface of the ovary, and after a 

 time ruptures, shedding the ovum into the abdominal cavity in the 

 neighbourhood of the Fallopian tube. This process is known as 

 ovulation. The rupture is brought about by cellular activity within 

 the follicle. The external wall of the follicle towards the surface of 

 the ovary is thinned away during the growth, so that it ruptures 



CORONA RAOIATA 



>.-jCYTOPLASi>. 



.-GERMINAL VESICLE 3J/,/ 

 1 (nucleus) 



YOLK SAC-- 



OLK QR/KNULES 

 ZONA R/kOIATA 



100 TIMES 



UMBILICAL CORO 



VNION 

 LEG BUO 



FIG. 475. THE PARTS OF A MATURE 

 HUMAN OVUM. DIAMETER -^ INCH. 

 (Keith, after Van der Stricht.) 



+ 3 TIMES 



FIG. 476. HUMAN EMBRYO AND ITS 

 MEMBRANES AT END OF FIRST 

 MONTH: EMBRYO ABOUT \ INCH, 

 THE ENVELOPE OF EMBRYONAL MEM- 

 BRANES ABOUT AN INCH. (Keith, 

 after Kellmann.) 



finally under the strain of the fluid secreted within the follicle. After 

 the rupture, the cells of the membrana granulosa proliferate to form 

 a yellowish tissue, known as the corpus luteum. Connective-tissue 

 septa carrying bloodvessels become developed in the corpus luteum. 

 The corpus luteum is normally about | inch in diameter. At the end 

 of three weeks it begins to diminish in size, so that it is a mere scar 

 at the end of two months, and is absent at the end of six months. 

 If, however, impregnation takes place, the corpus luteum grows in 

 size, until at the end of the second month it is l inch in diameter. 

 It remains this size until the sixth month of pregnancy, when it 

 gradually decreases in size and becomes converted into scar tissue. 

 The functions of the corpus luteum have already been mentioned 

 (p. 507). 



