21.4 Development of the internal genital organs

• Indifferent stage
• In males:
  • Differentiation of the canal system in the genital organ
  • Differentiation of the accessory sex glands
  • Differentiation of the urogenital sinus
• In females:
  • Differentiation of the canal system in the genital organ
  • Differentiation of the accessory sex glands
  • Differentiation of the urogenital sinus
• Summary: Development of the internal genital organs

In males: Differentiation of the urogenital sinus

In studies of the urinary system we have seen that the cloaca is subdivided by the uro-rectal septum into the rectum (dorsal) and the primary urogenital sinus (ventral).

The primitive urogenital sinus is in contact with the allantois. The upper part forms the future urinary bladder, while the middle and lower part forms the definitive urogenital sinus and, from it, the pelvic and phallic parts of the urethra (stage 17).

Fig. 39
The cloaca subdivides. Observe that the metanephros in this stage still lies quite caudally.

Fig. 40
The uro-rectal septum has subdivided the cloaca into the primary urogenital sinus (ventrally) and the rectum (dorsally).
Out of the primary urogenital sinus arise the urinary bladder and the definitive urogenital sinus.

Fig. 41
The spongy part of the urethra comes to a dead end in the outer section of the penis. Only in the 4th month does an epithelial lamella form from the tip of the penis to the blind end of the urethra. From this arises the urethra within the glans.