The diagram above illustrates a part of the human skeleton. The labelled part that provides surface for the attachment of the triceps is

The labelled part that provides a surface for the attachment of the triceps is part III. The triceps muscle is located at the back of the upper arm and is responsible for extending the arm at the elbow joint. It has three heads, and the long head of the triceps attaches to the scapula bone and the lateral and medial heads attach to the humerus bone of the upper arm. Part III of the diagram represents the humerus bone, and the bony protrusion on the back of the bone is called the olecranon process. This process provides a surface for the attachment of the tendon of the triceps muscle, allowing it to extend and straighten the arm at the elbow joint.