Testis are originally abdominal in a baby while it is in the mother's womb but become extra abdominal just before the time of birth?
Up to seven months of the baby development in the mother's womb, testis are present inside the abdomen. But just before the time of birth, testis descend down into scrotal sacs which lie externally below the abdomen. The reason for this is, testis cannot produce motile sperms if they are subjected to our normal body temperature. To reduce their temperature to 2 to 3 degrees centigrade below our body temperature, they were kept away from our body in scrotal sacs.