Cryptorchid is an animal that has had one or both testes remaining in the abdominal cavity that fails to descend into the scrotum. Cryptorchidism can either be unilateral, where one testicle fails to descend, or bilateral, where both testicles fail to descend. A cryptorchid still produces testosterone and will show stallionlike behaviors. Photo courtesy: Debra Hagstrom, University of Illinois.
For more information, see Stallion Anatomy Exam.