THE -EXTERNAL ORGANS. 



is connected witli the formation o-f the urogenital cord as an independent structure, 

 and results in the division of the cloaca into a dorsal or anal and a ventral or 

 urogenital part (urogemtal sinus). Somewhat later, in the ninth or tenth week, a 

 transverse integumental band completes the division, which band forms the whole ef 

 the perineum of the female, and the part of the perineal integument in the male 

 which is situated behind the scrotum. 



Of the two apertures the dorsal one or anus is of small size, and is surrounded by 

 a small circular integumental ridge ; the anterior or urogemtal aperture forms a 



Fig. 155. DEVELOPMENT OF THE EXTERNAL SEXUAL 



ORGANS IN THE MALE AND FEMALE FROM THE 

 INDIFFERENT TYPE. (Eckel'. ) 



A, the external sexual organs in an embryo of about 

 nine weeks, in which external sexual distinction is no~t 

 yet established, and the cloaca still exists ; B, the same 

 in an embryo somewhat more advanced, and in which, 

 without marked sexual distinction, the anus is now- 

 separated from the urogenital aperture ; C, the same in 

 an embryo of about ten weeks, showing the female type ; 

 D, the same in a male embryo somewhat more advanced. 

 Throughout the figures the following indications are 

 employed ; pc, sexual eminence (penis or clitoris) ; to 

 the right of these letters in A, the umbilical cord ; 

 p, penis ; c, clitoris ; cl, cloaca ; ug, urogenital open- 

 ing ; a, anus ; Is, cutaneous elevation which becomes 

 labium or scrotum ; I, labium ; s, scrotum ; co, caudal 

 or coccygeal elevation. 



-narrow vertical slit wider behind than before, and running forward as a furrow into 

 the rudiment of the penis, or clitoris. 



The well marked eminence in the integument which forms this rudiment, at first 

 indifferent in the two sexes, is surrounded by a deep circular fold of the integument 

 which encompasses its base, and which is the foundation of the mons veneris and 

 labia majora in the female, and when united by median fusion, of the scrotum in the 

 male.. The lips of the urogenital furrow, which in the female are converted into the 

 nymphae, and in the male unite as the integument below the penis, are both at first 

 precisely the same in all embryoes. In the open condition, which continues until 

 ^he eleventh or twelfth week, the parts appear alike in both sexes, and resemble 

 the more advanced female organs. The rudiments of Bartholin's or Coicper's 

 glands appear at an early period as involutions of epithelium, near the root of the 

 rudimentary clitoris or penis, on each side of the genito-urinary passage. 



In the female, the outer circular fold of integument enlarges at the sides so as to 

 cover the clitoris as the labia majora. The clitoris itself remains relatively small, 

 and the groove on its under surface becomes less and less marked, owing to the 

 opening out, and subsequent extension backwards, of its margins to form the nymplm. 

 The vascular bulbs, sunk more deeply in the tissues than in the male organ, remain 

 distinct and separate, except at one point where they run together in the glans 

 clitoridis. The hymen begins to appear about the fifth month as a fold of the lining 

 membrane at the opening of the genital passage into the urogenital sinus. Within 

 the vestibule, which is the shortened but widened remains of the urogenital sinus, 

 the urethral orifice is seen, the urethra itself undergoing considerable elongation. 



In the male, on the contrary, the penis continues to enlarge, and the margins of 

 the groove along its under surface gradually unite from the primitive urethral orifice 

 behind, as far forwards as the glans, so as to complete the long canal of the male 

 urethra, which is therefore a prolongation of the urogenital sinus. This is accom- 

 plished about the fifteenth week. When the union remains incomplete, the abnormal 



