THE EXTERNAL GENITALIA 



227 



tion of the male phallus, the open portion of the urogenital sinus also is 

 lengthened and forms the greater part of the penile urethra. In fetuses of 

 70 mm. (C R), the groove-like primitive urogenital opening, located in 

 the male near the glans and distant from the anus, begins to close and thus 

 forms a further portion of the urethra. The lips of the urogenital opening, 

 it will be remembered, correspond to the labia minora, or nymphce, of the 

 female. Finally, at 100 mm. (C H ?), the solid urethral plate of the glans 

 splits, forms a groove to the tip of the glans, and this groove in turn is 

 closed, continuing the urethra to the definitive openrng at the tip of the 

 glans (Fig. 237 C). Owing to the rapid elongation of the penis, there is 

 formed between its base and the anus an unpaired area, termed by Felix 



ABC 



FIG. 237. Three stages in the development of the male external genitals (after Tourneux 

 in Heisler). I, Penis; 2, glans; 3, urogenital groove; 4, genital swellings corresponding to labia 

 majora of female; 5, anus; 7, scrotal area with perineo-scrotal raphe. 



(1912) the the scrotal area, as it is the anlage of the scrotum (Fig. 237 A). 

 At 60 mm. (C H) this forms a median scrotal swelling, continuous laterally 

 with the paired genital swellings which form the labia majora in the fe- 

 male. When the scrotal sac develops in the scrotal area, the dense tissue 

 in the median line is stretched and forms the septum scroti. The attach- 

 ment of this septum forms an external median depression, the raphe. 

 The testes descend into the vaginal sacs of the scrotum through the paired 

 genital swellings, as described on p. 224, but the scrotum itself is an un- 

 paired structure derived from the scrotal area. After the descent of the 

 testes the genital swellings disappear (Fig. 237 C}. 



Comparing the male and female external genitalia, it is plain that the 

 glans penis and glans clitoridis are homologous. The labia minora cor- 

 respond to the phallic folds which close about the primitive urogenital 

 opening on the anal surface of the penis. The greater part of the shaft 

 of the male phallus does not develop in the female. On the other hand, 

 the genital swellings enlarge and become the mons pubis and labia majora 



