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[BOOK iv. 



condition as one of erection ; and the ripe follicle, whose ovum 

 is about to escape, bulges from its surface. The most projecting 

 portion of the wall of the follicle, which has previously become 

 excessively thin, is now ruptured, apparently by the mere dis- 

 tension of the cavity, and the ovum, now lying close under the 

 projecting surface of the follicle, escapes, invested by some 

 of the cells of the discus proligerus, into the Fallopian tube. 

 Much discussion has taken place as to how the entrance of the 

 ovum into the Fallopian tube is secured. It is probable that 

 under ordinary circumstances the ovary is embraced by the 

 trumpet-shaped fimbriated mouth of the Fallopian tube, and the 

 contact is probably rendered more complete by the turgid and 

 congested condition of both organs ; it is possible that the plain 

 muscular fibres present in the mouth of the tube may assist, 

 and indeed gliding movements of the mouth of the tube over 

 the ovary have been observed in animals. It has, however, been 

 asserted that the turgescerice of the tube does not occur until 

 after the ovum has become safely lodged in the tube, and it 

 is argued that the ovum is carried in the proper direction by cur- 

 rents set up by the action of the ciliated epithelium lining the 

 tube, currents whose direction and strength seem, as shewn by 

 experiment, to be adequate to carry into the uterus particles 

 present in the peritoneal fluid ; and the groove in the ciliated 

 surface of the ovarian fimbria especially connected with the 

 ovary, suggests itself as the natural path for the ovum. 

 Arrived in the tube, the ovum travels downwards very slowly, 

 by the action probably of the cilia lining the tube, though possi- 

 bly 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 ; the channel, 

 as we have seen, is a narrow one, especially at the entrance into 

 the uterus. The escape of the ovum is followed by changes in 

 the follicle and rest of the ovary, leading to the formation of a 

 corpus luteum. 



Concerning the exact nature of the changes in the uterus 

 which lead to the menstrual flow there has been and is much dis- 

 cussion. The opportunities for an exact histological investigation 

 of a human menstruating uterus are rare ; but from what has 

 been observed under the most favourable circumstances, aided 

 by the results of the study of the monkey which is subject to a 

 periodic change exceedingly like human menstruation, we may 

 conclude that the changes which occur are somewhat as follows. 

 In the first stage of the period not only does the whole uterus, 

 the cervix excepted, become congested, the blood vessels 

 being distended, and the mucous membrane especially red, thick 

 and swollen, but a new growth takes place in the mucous mem- 

 brane at least in its more superficial layers. This growth affects 

 not only the epithelial but also the connective tissue, stroma, 



