MENSTRUATION. 



839 



become excessively thin, is now ruptured, and the ovum, which having left 

 its earlier position, is lying close under the projecting surface of the follicle, 

 escapes, together with the cells of the discus proligerus (Fig. 216), into the 

 Fallopian tube. How the entrance of the ovum into the Fallopian tube is 

 secured is not exactly known. Some maintain that the ovary is grasped by 

 the trumpet-shaped fimbriated mouth of the Fallopian tube, itself turgid 

 and congested, the movement necessary to bring this about being effected 

 by the plain muscular fibres present in the mouth of the tube. Others, re- 

 jecting this view, and asserting that the turgescence of the tube does not 

 occur until after the ovum has become safely lodged in the tube, suggest 



FIG. 217. 



e f g h 



Successive Stages of the Formation of the Corpus Luteum in the Graafian Follicle of the Sow 

 (as seen in Vertical Section). At a is shown the state of the follicle immediately after the expul- 

 sion of the ovule, its cavity being filled with blood, and no ostensible increase of its epithelial 

 lining having yet taken place; at b a thickening of this lining has become apparent; at c it 

 begins to present folds, which are deepened at d, and the clot of blood is absorbed pari passu, and 

 at the same time decolorized ; a continuance of the same process, as shown at e,f, g, h, forms the 

 corpus luteum, with its delicate cicatrix. 



that the ovum is carried in the proper direction by currents in the peritoneal 

 cavity set up by the action of the ciliated epithelium lining the tube, cur- 

 rents whose direction and strength seem, as shown by experiment, to be 

 adequate to carry into the uterus particles present in the peritoneal fluid. 

 Arrived in the tube, the ovum travels downward, very slowly, by the action 

 probably of the cilia lining the tube, though possibly its progress may 

 occasionally be assisted by the peristaltic contractions of the muscular walls. 

 The stay of the ovum in the Fallopian tube may extend to several days. 

 There is an effusion of blood into the ruptured follicle, which is subsequently 

 followed by histological changes in the coats of the follicle resulting in a 

 corpus luteum 1 (Fig. 217). The discharge of the ovum is accompanied not 



1 [The following tabular statement by Dalton expresses the principal differences be- 

 tween the corpus luteum of the non-pregnant and pregnant female: 



CORPUS LUTEUM OF MENSTRUATION. ; CORPUS LUTEUM OF PREGNANCY. 



At the end of three 

 weeks. 



One Month. 

 Two Months. 



Six Months. 

 Nine Months. 



Three-quarters of an inch in diam- 

 eter; central clot reddish; convo- 

 luted wall pale. 



Smaller; convoluted wall bright yel- 

 low ; clot still reddish. 



Reduced to the condition of an insig- 

 nificant cicatrix. 



Absent. 

 Absent. 



Larger; convoluted with bright yel- 

 low; clot still reddish. 



Seven-eighths of an inch in diameter ; 

 convoluted wall bright yellow ; clot 

 perfectly decolorized. 



Still as large as at end of second 

 month ; clot fibrinous ; convoluted 

 wall paler. 



One-half an inch in diameter ; central 

 clot converted into radiating cica- 

 trix ; the external wall tolerably 

 thick and convoluted, but without 

 any bright yellow color.] 



