Decent of testes in Animals
During early fetal life, the testicles are situated against the dorsal wall of the abdomen in contact with the visceral surface of the kidneys, these testes descend in animals scrotum to fully function.
They are attached to the sub – lumbar region by a fold of peritoneum – the mesorchium containing vessels and nerves in its cranial border and in its caudal edge is the tail of the epididymis and two cords of fibrous tissue; one of these is short and connects the tail of the epididymis with the testicle which later becomes the ligamentum epididymis.
The other one is gubernaculum testis, which extends from the tail of the epididymis to the subperitoneal tissue in the vicinity of the future vaginal ring.
After the middle of fetal life, a pouch of peritoneum, the processus vaginalis, grows downward through the inguinal canal and carries with it fibres of the external cremaster muscle and inguinal extension of the gubernaculum testis.
Simultaneously the tail of the epididymis enters the processus vaginalis, followed by the testicle and mesorchium, till they reach the scrotum.
The gubernaculum blends with the subcutaneous tissue of the scrotum and forms the dartos.
In ruminants, descent takes place early and is completed at 3 months of fetal age. In the horse, the testes leave the abdominal cavity close to birth.
In dog, the testes are still in the lumbar area at the time of the birth and they descend into the scrotum shortly after birth. In the pig, descent occurs during fetal life and is completed shortly before birth.
Indefinite retention of the testicle, one or both, in the abdominal cavity or inguinal canal constitutes cryptorchism and such testes are non-spermiogenic.
It is common in pigs and horses. In some mammals it is normal as in the elephant and such animals are called testiconda.
