DEVELOPMENT OF THE GENITAL ORGANS. Ill 



perineum) begins to form and divides the cloaca into the anal cavity behind, 

 the urogenital sinus in front. In the sixth week a tubercle, the genital tubercle, 

 is formed in front of the cloaca, and this is soon surrounded by two folds of 

 skin, the genital folds. Towards the end of the second month the tubercle pre- 

 sents, on its lower aspect, a groove, the genital furrow, turned towards the 

 cloaca. All these parts are well developed at the period shown by No. III. of 

 the following diagrams, where the anus is separated from the urogenital sinus, 

 yet no distinction of sex is possible. 



Female Organs (Fig. 67, A, B, C). The female organs are developed by an 

 easy transition from the above form. The urogenital sinus persists as the ves- 

 tibule of the vagina, and forms a single tube with the upper part of the vagina, 

 which we have already seen developed from the united Mullerian ducts. The 

 genital tubercle forms the clitoris, the genital folds the labia majora, the lips of 

 the genital furrow, the labia minora, the genital furrow remaining open, except 

 below where it unites with the perineum, constituting the rapine*. 



Male Organs. In the male, the changes are greater from the indifferent type. 

 The genital tubercle is developed into the penis, the glans appearing in the 

 third month, the prepuce and corpora cavernosa in the fourth. The genital 

 furrow closes, and thus forms a canal, the spongy portion of the urethra. The 

 urogenital sinus becomes elongated, and forms the prostatic and membranous 

 urethra. The genital folds unite in the middle line, to form the scrotum, at 

 about the same time as the genital furrow closes, viz., between the third and 

 fourth month. 



