FIGURE 13. Testicular descent.

Left, Initial phase: the primitive gonad is located near the kidney, held by the cranial suspensory ligament (CSL) and the gubernaculum testis. Center, Transabdominal descent: androgen-mediated dissolution of the CSL and insulin like factor 3 (INSL3) mediated swelling of the gubernaculum bring the testis to the internal orifice of the inguinal canal. Right, Inguino-scrotal migration: the testis passes through the inguinal canal into the scrotum, this phase is androgen-dependent.

Reprinted from ref. 241: Klonisch T, Fowler PA, Hombach-Klonisch S. Molecular and genetic regulation of testis descent and external genitalia development. Developmental Biology, 270:1-18 (2004), Copyright 2004, with permission from Elsevier. http://www.sciencedirect.com/science/article/pii/S001216060400137X