Final answer:
The torn piece of muscle attached on the medial side near the angle of the mandible is most likely the medial pterygoid, which is crucial for the side-to-side movement of the mandible during mastication.
Step-by-step explanation:
If a torn piece of muscle is attached on the medial side near the angle of the mandible, the muscle in question is most likely the medial pterygoid. Among the options given, the medial pterygoid muscle is known for its action that moves the mandible from side to side, which is essential during the process of mastication or chewing. This muscle works together with the masseter, temporalis, and lateral pterygoid muscles to assist in the complex movements required for chewing.