[Music] in this lesson I will review the supinator muscle which is a key muscle of the extensor group in order to understand the complex anatomy of this we'll start with a line drawing of the right elbow joint and we have an anterior vantage point the supinator muscle has two areas of attachment the first comes from the proximal ulna as seen here and the muscle wraps around the posterior part of the proximal radius and therefore is hidden from our view a hint of that muscle is seen by the dashed lines the second component of this muscle has its attachment on to the distal humerus as seen here both of these components unite and the fibers then wrap around the proximal radius to attach onto its anterior surface so this is the supinator muscle here this is one of its attachment coming from the humerus and then there is the other attachment from the ulna this muscle participates in the action of supination of the forearm let's look at a dissection photograph here of the right elbow region and the proximal forearm this may be a little confusing so let me orient you to this the posterior part of this specimen is seen on this side of the screen while the anterior part is seen on this side of the screen so orient yourself again mentally the we're looking at the right elbow region as well as the proximal forearm the anterior is towards the right side of your screen and therefore the palm which is just below and out of our view is facing towards the right side of the screen and in order to orient ourselves further let's put the muscles on the anterior side of the arm the flexor group of muscles over here this will be the end here group of flexor muscles of the arm which crosses the elbow joint and attaches on to the proximal forearm bones in order to be a flexor this was the brachialis muscle the supinator muscle is actually seen over here and all of this is the supinator muscle it has an attachment on to the distal humerus as well as on the ulna and then the muscle wraps around with its oblique course on to the proximal radius specifically on its anterior surface note a very important relationship with a nerve in this case the radial nerve which is coming down the anterior part of the arm here crosses the elbow joint so this is the radial nerve and then it divides into two branches a superficial and a deep branch the deep branch of the radial nerve also called the posterior interosseous nerve dives into the supinator muscle as seen in the photograph the superficial branch of the radial nerve is a sensory or cutaneous branch and it runs down the forearm superficial to the supinator muscle but is covered by some of the other muscles that are also part of the extensor group specifically the brachioradialis muscle so this is a view of the supinator muscle and if summarizes some of its key anatomical relationships [Music] you