Anconeus muscle

The anconeus muscle (or anconaeus/anconæus) is a small triangular muscle placed behind and below the elbow joint, and seems to be continuous by its upper margin with the lateral part of the triceps. Some consider anconeus to be a continuation of the triceps brachii muscle. Some sources consider it to be part of the posterior compartment of the arm, while others consider it part of the posterior compartment of the forearm. The anconeus muscle can easily be palpated just lateral to the olecranon process of the ulna. (Wikipedia)