ANATOMICAL FEATURES 



SUPRARENAL 



Fig. 3. Diagrammatic representations of the urogenital structures in the developing 

 male pig, with special emphasis upon testicular descent. (A) Early relationship of the 

 genital fold (genital ridge), mesonephric kidney and its duct, together with the meta- 

 nephric kidney and the ureter in 20-mm. pig embryo. The relationship of the mesonephric 

 and metanephric ducts to the urogenital sinus is shown. The MiJllerian duct is omitted. 

 (B) Male pig embryo about 45-mm., crown-rump length, showing relationship of gonad 

 and metanephric kidney. The metanephric kidney is shown below (dorsal to) the meso- 

 nephric kidney. The gonad (testis) is now a well-defined unit. The portion of the genital 

 fold tissue anterior to the testis becomes the anterior suspensory ligament of the testis, 

 while the genital fold tissue caudal to the testis continues back to join the inguinal liga- 

 ment of the mesonephros (the future gubernaculum). (C) About 80-mm., crown-rump, 

 pig embryo. Observe that the metanephros is now the dominant urinary organ and has 

 grown cephalad, displacing the mesonephric kidney which is regressing and moving 

 caudally with the testis. The remains of the mesonephric kidney at this time are gradually 

 being transformed into epididymal structures. (D) About 130-mm.. crown-rump, pig 

 embryo. Observe that the test-is is approaching the internal opening of the inguinal canal. 

 The anterior suspensory ligament is now an elongated structure extending over the latero- 

 ventral aspect of the metanephric kidney; the gubernacular tissue is shown extending 

 downward into the inguinal canal. (E) Later stage in testicular descent. The anterior 

 suspensory ligament of the testis is a prominent structure, while the gubernaculum is 

 compact and shortened. (F) The condition found in the full-term, fetal pig. The testis 

 is situated in the scrotal swelling; the gubernaculum is much shortened, while the anterior 

 suspensory ligament remains as a prominent structure, extending cephalad to the caudal 

 portions of the metanephric kidney. 



2. Possible Factors Involved in Testis Descent 

 The descent of the testis within the peritoneal cavity and into the scrotum 

 poses an interesting problem. In embryonic development extensive migration 

 of cell substance, or of cells, tissues, and organ structures is one of many 

 processes by which the embryonic body is formed. That is to say, the dynamic 

 movement or displacement of developing body structures from their original 

 position is a part of the pattern of development itself. The casual factors in- 



