What is the name of the irregular shape just past the oval window?

The irregular shape just past the oval window is the cochlea. The cochlea is a spiral-shaped, fluid-filled structure in the inner ear that plays a critical role in the process of hearing. Once sound waves enter through the oval window, they transfer to the fluid within the cochlea, which then stimulates hair cells that convert these vibrations into electrical signals sent to the brain.

The scala vestibule, mentioned in the choice you selected, is actually one of the chambers within the cochlea. It is located above the cochlear duct and is part of the fluid system within the cochlea that helps facilitate the movement of sound waves through the inner ear. Understanding the structure of the cochlea and its components is essential in the study of hearing and the mechanisms involved in sound perception.