ORIGIN
Since there are three parts in the triceps, there are three origins. The long heads' origin is from the infraglenoid tubercle of the scapula, and extends to the teres major and teres minor. The medial heads' origin is located on the lower half posterior humerus inferomedial to both the intermuscular septa. It is usually covered by the long and the lateral head, therefore making it less visible. The lateral heads' origin is located at the upper half posterior humerus.
INSERTION
The olecranon process
Even though the triceps have three different origins, it only has one insertion. The heads converge to a single tendon and eventually inserts into the posterior Olecranon Process of the ulna.