Final answer:
The subscapularis is a rotator cuff muscle that originates from the subscapular fossa and inserts into the lesser tubercle of the humerus, where it performs medial rotation and stabilization of the shoulder joint.
Step-by-step explanation:
The subscapularis muscle is one of the four rotator cuff muscles that provide primary support to the shoulder joint. It originates from the subscapular fossa located on the anterior side of the scapula and inserts into the lesser tubercle of the humerus. Besides medially rotating the shoulder, it also plays a crucial role in stabilizing the head of the humerus within the glenoid cavity. This function is vital for preventing dislocation and maintaining the integrity of the shoulder joint during various arm movements.
The four rotator cuff muscles, including the subscapularis, attach to the greater or lesser tubercles of the humerus, encompass the head of the humerus, and fuse with the walls of the articular capsule, forming the rotator cuff. This unique arrangement acts as dynamic ligaments to provide structural support and facilitate complex shoulder movements. Additionally, the subscapular and subacromial bursae minimize friction between muscle tendons and the scapula.