Final Answer:
The bulbospongiosus muscles are erectile tissue structures which extend from the tuber ischii to the cranial surface of the urethra as it crosses from behind the ischiatic arch.
Step-by-step explanation:
The bulospongiosus muscles are indeed erectile tissue structures. They play a crucial role in sexual function by aiding in the process of erection. These muscles extend from the tuber ischii, which is part of the pelvic bone, to the cranial surface of the urethra. This anatomical connection is vital for their function in the male reproductive system. The description mentions that these muscles cross from behind the ischiatic arch, highlighting their specific anatomical location in the pelvic region.