The gubernaculum during testicular descent in the human fetus.

This study of 178 male human fetuses and infants demonstrates that descent of the testis through the inguinal canal is a rapid process, with 75% of testes descending between 24 and 28 weeks of gestation. The gubernaculum is a cylindrical, gelatinous structure attached cranially to the testis and epididymis. While the testis is in the abdomen, the caudal tip of the gubernaculum is firmly attached to the region of the inguinal canal. In a few fetuses prior to descent the globular tip of the gubernaculum can be seen bulging through the external inguinal ring, covered by superficial fascia, with no macroscopically discernible extensions to the scrotum or any other area. Once the testis has passed through the inguinal canal, the bulbous lower tip of the gubernaculum is no longer firmly attached to any structure, nor does it extend to the bottom of the scrotum. Histologically the gubernaculum consists of undifferentiated mesenchymatous tissue. Prior to descent of the testis, there is an increase in the length of the intra-abdominal gubernaculum. The wet mass of the gubernaculum relative to the fetal mass increases rapidly prior to descent, while the relative wet mass of the testis remains constant during this period. There is also an increase in the wet/dry mass ratio of the gubernaculum, denoting an increase in its water content prior to descent. This indicates that a combination of growth processes is responsible for testicular descent, with the increase in the size of the gubernaculum playing the most important role in passage of the testis through the inguinal canal.