Musculus comitans nervi mediani (M. palmaris profundus)

Palmaris profundus muscles were found in two cadavers during routine dissection of the upper limb. This rare muscle was found in two forms. In the first case, the muscle resembled a diminutive palmaris longus with the belly arising from the common flexor tendon. In the second case however, a reversed muscle with the belly emerging from beneath the transverse carpal ligament and its long thin tendon extended to and inserted in the common flexor tendon. The similarity therefore of these muscles to variable forms of palmaris longus is remarkable but they differed in one very important aspect from palmaris longus. The muscles are of special interest because, in both cases, the muscles were found enclosed in a common fascial sheath with the median nerve. These unusual muscles, in spite of mimicking palmaris longus, may perhaps, be better named "musculus comitans nervi mediani" to denote their very important relationship to the median nerve, that of being the intimate traveling companion of the median nerve through the forearm and into the hand by way of the carpal canal beneath the transverse carpal ligament. In one case, a well developed median artery was also found which also entered the carpal canal along with the median nerve and its muscular companion.