THE EXTERNAL GENITALIA 227 



forms the greater part of the penile urethra. In fetuses of 70 mm. (C R) the 

 groove-Kke 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 failure of this opening to close gives rise to an anomaly known 

 as hypospadias. The lips of the urogenital opening, it will be remembered, corre- 

 spond to the labia minora or nympha of the female. Finally, at 100 mm. (C H ?), 

 the solid urethral plate of the glans sphts, forms a groove to the tip of the glans, 

 and this groove in turn is closed, continuing the urethra to the definitive open- 

 ing at the tip of the glans. Owing to the rapid elongation of the penis, there is 

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

 scrotal area, as it is the anlage of the scrotum. At 60 mm. (C H) this forms a 

 median scrotal swelhng, continuous laterally with the paired genital swellings 

 which form the labia majora in the female. When the scrotal sac develops in the 

 scrotal area, the dense tissue in the median line is compressed and forms the 

 septum scroti. The attachment of this septum forms an external median depres- 

 sion. The testes descend into the vaginal sacs of the scrotum through the 

 paired genital swellings, as described on p. 223, 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 correspond to the 

 phallic folds which close about the primitive urogenital opening and the anal 

 surface of the penis. The greater part of the stem of the male phallus does not 

 develop in the female. On the other hand, the genital swelUngs enlarge and be- 

 come the mons pubis and labia majora of the female, while in the male they are 

 only temporary structures. The scrotum does not develop in the female, being 

 represented only by the posterior commissure of the labia majora. 



Accessory Glands. — The prostate gland develops in both sexes as entodermal 

 outgrowths of the urogenital sinus (urethra) both above and below the entrance 

 of the male ducts. The tubules arise in five distinct groups and total an average 

 number of 63 (Lowsley, Amer. Jour. Anat., vol. 13, 1912). In the male the 

 surrounding mesenchyme differentiates both white fibrous connective tissue and 

 smooth muscle fibers into which the anlages of the prostate grow. In the female 

 the tubules remain isolated. The prostatic anlages appear in male fetuses of 

 55 mm. (C H), chiefly as dorsal and lateral outgrowths. Two- thirds of the 

 tubules are caudal to the openings of the male ducts. In the female the gland is 

 rudimentary {paraurethral ducts), the maximal number of outgrowths being three. 



