VAN 211: Veterinary Histology and Embryology (2+2)

EXTERNAL GENITALIA

• Embryos of six weeks present a conical genital tubercle in the mid-ventral line between the umbilical cord and tail. Its caudal slope bears a shallow urethral groove, flanked on either side by slightly elevated urethral folds.
• The genital tubercle elongates into a cylindrical phallus whose tip is rounded into glans. Lateral to the phallus on either side appears a rounder ridge- the labio-scrotal swelling.
• Rupture of the urethral membrane in the floor of the-urethral groove provides an external opening for the urino-genital sinus. So far the development is identical in both the sexes.
• In the male, the phallus elongates to become the penis. The edges of the urethral groove progressively fold together in a distal direction to transform an open urino-genital sinus into the tubular urethra within the penis. The fused edges form the raphe. The scrotal swellings shift laterally and behind and develop into the scrotum. Each half of the scrotum is separated from its mate by a septum and a superficial raphe.
• In the female, the phallus lags in development and becomes the clitoris. The shorter urethral groove remains as the vestibule and the urethral folds constitute the labia minora. The primitive labio-scrotal swelling enlarge and fuse below the anus in the dorsal commissure, while the swellings enlarge to form the labia-majora.

Anamolies

• Hypospadias - failure of closure of the lips of the urethral grooves, on the ventral surface of the penis.
• Epispadias -urethra opening on the dorsal surface of the penis due to displacement of the cloacal membrane.