Which of the following structures is not typically considered involved with TMJ function?

The middle portion of the disc is not typically considered involved with TMJ function in the same way as the other structures listed. The temporomandibular joint is a complex structure where various components work together to facilitate movement and function.

The capsule is crucial as it encloses the joint and provides stability, while the muscles, particularly the ones involved in mastication, are essential for the movement of the jaw. Retrodiscal tissue plays an important role too, as it helps in cushioning and supporting the disc during jaw movements.

In contrast, while the middle portion of the disc influences the overall function of the TMJ, it does not play a direct or active role in the movement or dynamic function of the joint. Rather, it acts more as a passive structure, accommodating movements rather than aiding them directly. Thus, it is not typically regarded as functionally involved compared to the other elements that have more dynamic roles in the TMJ.