EXTERNAL ORGANS OF GENERATION. 613 



ceives the inferior opening of the urethra and vagina, and is bounded 

 anteriorly by the commissure, superior, and posteriorly by the commis- 

 sura inferior. Stretching across the posterior commissure is a small 

 transverse fold, thefranulum labiorum or fourchette, which is ruptured 

 during parturition, and immediately within this fold is a small cavity, 

 the fossa navicularis. The breadth of the perineum is measured from 

 the posterior commissure to the margin of the anus, and is usually 

 not more than an inch across. The external surface of the labia is 

 covered with hairs ; the inner surface is smooth, and lined by mucous 

 membrane, which contains a number of sebaceous follicles, and is 

 covered by a thin cuticular epithelium. The use of the labia majora 

 is to favour the extension of the vulva during parturition ; for, in the 

 passage of the head of the foetus, the labia are completely unfolded 

 and effaced. 



The Labia minora, or nymphce, are two smaller folds situated within 

 the labia majora. Superiorly they are divided into two processes, 

 which surround the glans clitoridis, the superior fold forming the 

 praeputium clitoridis, and the inferior its fraenulum. Inferiorly, they 

 diminish gradually in size, and are lost on the sides of the opening of 

 the vagina. The nymphae consist of mucous membrane, covered by 

 a thin cuticular epithelium. They are provided with a number of 

 sebaceous follicles, and contain, in their interior, a layer of erectile 

 tissue. 



The Clitoris is a small elongated organ situated in front of the ossa 

 pubis, and supported by a suspensory ligament. It is formed by a 

 small body, which is analogous to the corpus cavernosum of the penis, 

 and, like it, arises from the ramus of the os pubis and ischium on each 

 side, by two crura. The extremity of the clitoris is called its glans. 

 It is composed of erectile tissue, enclosed in a dense layer of fibrous 

 membrane, and is susceptible of erection. Like the penis, it is pro- 

 vided with two small muscles, the erectores clitoridis. 



At about an inch beneath the clitoris is tlie entrance of the vagina. 

 an elliptical opening, marked by a projecting margin. The entrance to 

 the vagina is closed in the virgin by a membrane of a semilunar form, 

 which is stretched across the opening ; this is the hymen. Sometimes 

 the membrane forms a complete septum, and gives rise to great incon- 

 venience by preventing the escape of the menstrual effusion. It is 

 then called an imperforate hymen. The hymen must not be considered 

 a necessary accompaniment of virginity, for its existence is very un- 

 certain. When present it assumes a variety of appearances : it may 

 be a membranous fringe, with a round opening in the centre, or a 

 semilunar fold, leaving an opening in front ; or a transverse septum, 

 having an opening both in front and behind ; or a vertical band with 

 an opening at either side. 



The rupture of the hymen or its rudimentary existence, gives rise 

 to the appearance of a fringe of papillae around the opening of the 

 vagina : these are called carunculce myrtiformes. 



The triangular smooth surface between the clitoris and the entrance 



