What muscle is below the deltoid and is attached to the ulnar process? how many heads does this muscle have?

Triceps is the muscle that is located below deltoid muscle and its inserted in the olecranon process of ulna. This muscle do have three origins and one insertion.

Triceps is the muscle that is responsible for the extension of elbow joint and also contribute to extension of shoulder joint. This muscle have three origin, that's why the name triceps. The triceps muscle has three heads which are:

A. The long head originates from the infraglenoid tubercle of scapula.

B. The lateral head originates from above the radial Grove in humerus.

C. The medial head originates form below the radial Grove in humerus.

These heads meet to form the body of triceps which gets inserted as triceps tendon in the olecranon process of ulna just behind the elbow. The contraction of this muscle causes the extension of the elbow joint.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.