900 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Domestication has, however, interfered with the original plan of nature. 

 It has rendered the lower forms more prolific and has made more frequent 

 their reproductive periods. Civilization has done exactly the same for woman. 

 It has rendered her more prolific and has made more frequent her reproduc- 

 tive periods. It is wholly probable that the menstrual periods of woman are 

 the homologues of the frequent reproductive periods of the lower forms. It 

 has been seen that the latter are characterized by the same kind of phenomena 

 that exist in the former ; the characteristic human menstrual phenomena are 

 least developed in the lower mammals, much more so in the monkey, and are 

 most pronounced in the human female. For what purpose this evolution of 

 function has taken place we do not know. Below the human species concep- 

 tion is confined to these times of " heat ; " in woman it is possible at other 

 than her menstrual periods. In this respect woman is more highly endowed 

 than her mammalian ancestors. 



The Vagina. The vagina (Fig. 309, vg] is the broad passage from the 

 uterus to the external organs. Its walls consist of smooth muscle fibres, 

 arranged both circularly and longitudinally. It is lined by stratified scaly 

 epithelium and is surrounded by erectile tissue. Its walls contain few glands. 

 Its specific functions are connected solely with the reproductive process ; in 

 copulation it receives the penis and the semen. Its cavity is the pathway out- 

 ward for the products of menstruation and, in parturition, for the child. 



The Vulva and its Parts. The vulva (Fig. 309) comprises the genital 

 organs that are visible externally viz. the mons Veneris, the labia majora (Lm), 

 the labia minora or nymphce (n), the clitoris, which is the diminutive homologue 

 of the penis of the male, and the hymen (A), or perforated curtain that guards the 

 entrance to the vagina and is usually ruptured at tho time of the first coition. 

 The vulva receives the openings of the vagina, the urethra (u), and the ducts of 

 Bartholini's glands. Its parts are capable of turgidity through its rich vas- 

 cular supply, and perform minor ill-defined, adaptive, and stimulating func- 

 tions in copulation. Their surface is covered by mucous membrane which is 

 moistened and lubricated by a secretion from numerous mucous follicles, seba- 

 ceous glands, and the glands of Bartholini. The latter are comparable to 

 Cowper's glands of the male and secrete a viscid fluid. 



The Mammary Glands. The mammary glands, being active only during 

 the period of lactation, may best be studied in connection with that function 

 (see p. 201). 



Internal Secretion. A priori, the reproductive organs can scarcely be 

 regarded as organs that are quiescent during the greater part of life and pas- 

 sively await the reproductive act. The view that they are more than this is 

 supported by some, although slight, experimental evidence. Notwithstanding 

 the fact that removal of the testis or the ovary in adult life is often unaccom- 

 panied by great somatic changes, the profound effects of early castration upon 

 development, in both the male and female, show that upon the presence of the 

 sexual organs depends the appearance of many of the secondary sexual cha- 

 racters characters which apparently are independent of those organs, and yet 



