Flexor Digitorum Superficialis
The Flexor Digitorum Superficialis is the largest superficial muscle in the forearm. It forms an intermediate layer between the superficial and deep groups of forearm muscles.
This is an important landmark for the median nerve, which travels distally on its deep surface. To test flexor digitorum superficialis, one finger is flexed at the proximal interphalangeal joint against resistance and the other fingers are held in an extended position, thereby inactivating flexor digitorum profundus.