74 THE PHYSIOLOGY OF REPRODUCTION 



The vulva comprises the female generative organs which are 

 visible externally. These include the mons veneris, the labia major 

 and minora, and the clitoris. The last-mentioned structure is a 

 small erectile organ, which is homologous with the penis. 1 (See 

 Chapter VII., p. 261.) 



In giving an account of the changes which take place in the 

 uterus during the menstrual cycle of the human female, it will be 

 convenient to adopt the scheme of classification employed by Milnes 

 Marshall 2 in his work on " Vertebrate Embryology." This classifica- 

 tion, as will be seen later, is identical with that adopted by Heape 3 in 

 describing the menstrual changes of monkeys. The cycle is divided 

 into four stages, as follows : 



(1) The Constructive Stage. 



(2) The Destructive Stage. 



(3) The Stage of Repair. 



(4) The Stage of Quiescence. 



The last stage may conveniently be considered first. 



The Stage of Quiescence. The normal condition of the human 

 endometrium has been described by Webster, 4 to whose account 

 the reader is referred. This author calls special attention to the 

 following points : (1) The thickness of the inucosa is not uniform, 

 but varies considerably. (2) The epithelial cells which line the 

 mucosa, and also those which line the glands, show differences in 

 shape and size, and in the position of the nuclei. (3) The epithelial 

 cells lining the glands are, as a rule, larger than the superficial 

 cells. (4) The interglandular connective tissue or stroma is mainly 

 embryonic in nature, and consists of a nucleated protoplasmic 

 reticulum, containing every stage of transformation into the more 

 differentiated spindle-shaped cells. (5) The stroma nearest the 



that it may have been useful in the earlier history of the race, when sexual 

 intercourse probably occurred at an early age, before the reproductive organs 

 were mature. Under such circumstances the hymen, instead of being a 

 barrier, may have facilitated successful coitus. Metchnikoff supposes the 

 aperture to have become gradually dilated by repeated intercourse without 

 being torn, until it admitted of the entrance of the adult male organ. 



1 The triangular space above the orifice of the vagina into which the 

 female urethra opens is often called the vestibule. 



2 Milnes Marshall, Vertebrate Embryology, London, 1893. 



3 Heape, "The Menstruation of Semnopithecus, etc.," Phil. Trans., B., 

 vol. clxxxv., 1894, and vol. clxxxviii., 1897. A similar classification has been 

 adopted by Minot (Human Embryology, 1892), who divides the menstrual 

 process into (1) Tumefaction ; (2) Menstruation ; and (3) Restoration of the 

 mucosa. 



4 Webster, Human Placentation, Chicago, 1901. 



