954 



MENSTRUATION. 



are obliterated at this point and the tissue undergoes atrophy, so that with 

 increasing pressure rupture must take place here. 



After menstruation, the epithelium of the uterine mucosa is regenerated 

 by indirect division, particularly from the sixteenth to the eighteenth day after 

 the beginning of menstruation; the premenstrual swelling of the mucosa begins 

 again between the eighteenth and the nineteenth day. 



In individual cases ovulation and the formation of the menstrual decidua 

 may take place independently; so that menstruation may occur without ovulation 



(more frequent) or ovulation without menstrua- 

 tion (seldom). Menstrual bleeding occurs only 

 in the presence of ovarian tissue and a 

 sufficient development of the uterine mucosa. 

 Although many facts tend to support this new 

 conception, there still remains the difficulty that 

 in animals that have several placental sites (for 

 example the cow), bleeding takes place from 

 these situations at the time of heat. 



Formation of the Corpus Luteum. The 

 follicle whose contents have been discharged 

 collapses. In its interior there remains the lining 

 of granulosa-cells and a small amount of blood, 

 which quickly coagulates. The small wound of 



rupture undergoes cicatrization after the serum has been absorbed. The wall of 

 the follicle, which has become vascular, now swells as a result of mitotic division 

 of the cells of the inner thecal wall and forces inward villous granulations of young 

 connective tissue (Fig. 367), rich in capillaries and cells. Leukocytes wander 

 into the cavity. Lutein-cells are formed anew through proliferation of the in- 

 ternal connective tissue layer of the wall of the follicle (Fig. 366). The corpus 

 luteum is not an epithelial, but a connective tissue structure. Internal to the 

 lutein-cells a layer of connective tissue develops later on. The lutein-cells subse- 

 quently undergo degeneration and there remains a cicatricially contracted "cor- 

 pus albicans." The capsule becomes gradually more and more fused with the 

 ovarian stroma. 



FIG. 366. Lutein-cells from the Corpus 

 luteum of the Cow (after His). 



Stroma of the ovary with 

 vascular spaces. 



Corpus luteum with fibrous 

 center. 



Lymph-vessels. 



FIG. 367. Corpus luteum of the Cow, enlarged one and one-half times (after His). 



Should pregnancy not occur after the menstruation, absorption of the fat 

 formed takes place, with the formation of a crystalline body formerly supposed 

 to be hematoidin, but shown to be lutein or lipochrome, and of other pigment- 

 derivatives, while the yellow body undergoes uniform contraction within four 

 weeks, down to a small remnant. Such yellow bodies, when pregnancy does 

 not subsequently take place, are designated spurious corpora lutea. If, however, 

 pregnancy results, the size of the body, in accordance with the greatly increased 

 formative processes, is quite considerable (especially in the third or fourth month). 



