The triceps brachii is a large muscle that covers the entire back side of the upper arm. It is divided into three sections, known as the lateral (outer) head, medial (middle) head, and long (inner) head.
Origin
The medial head of the triceps originates on the lower portion of the back of the humerus over a wide space extending nearly two-thirds of the length of the bone.
Insertion
All three heads come together into a common tendon which inserts on the olecranon process of the ulna.
Function
Elbow joint extension.
