The Shoulder Joint is made up of 5 muscle.

1. Deltoid - The big bulky muscle seen outside
2. Supraspinatus
3. infraspinatus
4. Teres Minor
5. Subscapularis

Muscles 2 to 5 are called the rotator cuff muscles.

The long head of biceps tendon runs inside the shoulder and attaches to the upper part of the glenoid (the shoulder joint socket).