570 GENERATION AND DEVELOPMENT. 



inner surface of the uterus, and mixed with mucus from the 

 uterus, vagina, and external parts of the generative apparatus. 

 Being diluted by this admixture, the menstrual blood coagu- 

 lates less perfectly than ordinary blood ; and the frequent 

 acidity of the vaginal mucus tends still further to diminish its 

 coagulability. This has led to the erroneous supposition that 

 the menstrual blood contains an unusually small quantity of 

 fibrin, or none at all. The blood-corpuscles exists in it in their 

 natural state : mixed with them may also be found numerous 

 scales of epithelium derived from the mucous passages along 

 which the discharge flows. 



Corpus Luteum. 



Immediately before, as well as subsequent to, the rupture of 

 a Graafian vesicle, and the escape of its ovum, certain changes 

 ensue in the interior of the vesicle, which result in the produc- 

 tion of a yellowish mass, termed a corpus luteum. 



When fully formed the corpus luteum of mammiferous 

 animals is a roundish solid body, of a yellowish or orange color, 

 and composed of a number of lobules, which surround, some- 

 times a small cavity, but more frequently a small stelliform 

 mass of white substance, from which delicate processes pass as 

 septa between the several lobules. Very often, in the cow and 

 sheep, there is no white substance in the centre of the corpus 

 luteum ; and the lobules projecting from the opposite walls of 

 the Graafian vesicle appear in a section to be separated by the 

 thinnest possible lamina of semi-transparent tissue. 



When a Graafian vesicle is about to burst and expel the 

 ovum, it becomes highly vascular and opaque ; and, immedi- 

 ately before the rupture takes place, its walls appear thickened 

 on the interior by a reddish glutinous or fleshy-looking sub- 

 stance. Immediately after the rupture, the inner layer of the 

 wall of the vesicle appears pulpy and flocculent. It is thrown 

 into wrinkles by the contraction of the outer layer, and, soon, 

 red fleshy mammillary processes grow from it, and gradually 

 enlarge till they nearly fill the vesicle, and even protrude from 

 the orifice in the external covering of the ovary. Subsequently 

 this orifice closes, but the fleshy growth within still increases 

 during the earlier period of pregnancy, the color of the sub- 

 stance gradually changing from red to yellow, and its con- 

 sistence becoming firmer. 



The corpus luteum of the human female (Fig. 211) differs 

 from that of the domestic quadruped in being of a firmer tex- 

 ture, and having more frequently a persistent cavity at its 

 centre, and in the stelliform cicatrix, which remains in the 



