THE ABDOMEN 635 



The hymen appears as a semilunar fold of mucous membrane, 

 extending as a rule over the dorsal part of the external orifice of 

 the vagina. 



The glands of Bartholin are developed laterally as evaginations of 

 the epithelial lining of the caudal part of the uro-genital sinus, 

 which part, when expanded, forms the vestibule. 



The bulhi vestibuli and the pars inter media of Kobelt are developed 

 as masses of erectile tissue close to the labia minora or n^nnphae 

 and clitoris. 



Male External Organs. — In the male the genital eminence under- 

 goes considerable lengthening, and gives rise to the corpora cavernosa 

 penis, the terminal enlargement of the eminence forming the glans 

 penis. As the genital eminence elongates, the genital groove on 

 its lower surface undergoes proportionate elongation, and at the 

 same time deepens. The internal genital folds, which form the 

 lateral lips of this groove, and which in the female remain separate 

 from each other as the labia minora, come together in the male, and 

 fuse over the genital groove. This groove is thus transformed into 

 a canal, which constitutes the spongy part of the male urethra. 

 The line of fusion of the internal genital folds is indicated, in adult 

 life, by the median raphe, which traverses the under, or scrotal, 

 aspect of the penis. The portion of the urethra within the glans 

 penis is developed from a collection of ectodermic cells, forming 

 the so-called urethral septum or plate. These cells become tun- 

 nelled into a canal, which is continuous with the spongy urethra, 

 developed as stated from the genital groove. 



The spongy part of the urethra extends as far as the uro-genital 

 sinus, from the lower part of which the prostatic and membranous 

 purls of the canal are developed. 



In rare cases the internal genital folds fail to unite over some 

 portion of the genital groove. In such cases the spongy urethra 

 opens externally on the under, or scrotal, aspect of the penis, and 

 the condition is known as hypospadias. 



The internal genital folds, which enclose the spongy part of the 

 urethra, acquire erectUe tissue and constitute the corpus spongiosum 

 penis. The genital eminence, having lengthened considerably, and 

 having acquired erectile tissue, gives rise by its greater part to the 

 corpora cavernosa penis, whilst its terminal enlargement forms the 

 glans penis. As just stated, the corpus spongiosum penis is formed 

 by the fusion of the two internal genital folds, this fusion converting 

 the genital groove into the spongy part of the urethra. 



The external genital folds, which in the female remain separate 

 and form the labia majora, unite in the male and give rise to the 

 scrotum. The line of fusion is indicated, in adult life, by the scrotal 

 raphe. 



It is to be noted that, whilst the prostatic and membranous 

 portions of the male urethra are developed from the lower part of 

 the urogenital sinus, and are therefore non-penile, the spongy 

 portion of the canal is developed from (i) the genital groove on the 



