Anat Cell Biol.  2023 Mar;56(1):150-154. 10.5115/acb.22.141.

An accessory muscle of flexor digitorum profundus with bipennate first lumbrical: a unique variation of clinical significance

  • 1Department of Anatomy, All India Institute of Medical Sciences, Hyderabad, Telangana, India


During the deep dissection of the front of the forearm, an anomalous accessory muscle in relation to the flexor digitorum profundus (FDP) muscle was observed in the right forearm. The accessory muscle consisted of a spindle-shaped muscle belly with a long tendon underneath the flexor pollicis longus muscle. When followed distally, the accessory muscle tendon was found lateral to the FDP tendon for the index finger and entered the palm deep to the flexor retinaculum. In the palm, we encountered the first lumbrical muscle as a bipennate muscle taking origin from the adjacent sides of the middle of the tendons of FDP and accessory muscle tendon. After giving origin to first lumbrical muscle, the accessory muscle got merged with the tendon of FDP for index finger. Understanding this kind of variation is required for radiologists and hand surgeons for diagnostic purposes and while performing corrective surgical procedures.


Accessory muscle; Bipennate; Forearm; Gantzer muscles; Lumbricals


  • Fig. 1 Showing accessory muscle of right flexor compartment of the forearm with half belly and half tendon. AcM, Accessory muscle; FDP, flexor digitorum profundus; FPL, flexor pollicis longus; FR, flexor retinaculum; CT, carpal tunnel; AcMTn, accessory muscle tendon; 1st LB, first lumbrical; Br-MN, branch of median nerve.

  • Fig. 2 Showing AcMTn of front of right forearm, lying lateral to the FDPTn. Attachment of bipennate 1st LB can be seen from its deeper aspect lying superficial to ADP. AcMTn, accessory muscle tendon; FDPTn, tendon of the Flexor Digitorum Profundus; 1st LB, first lumbrical; ADP, adductor pollicis; DTs, digital tendons; HThr Ms, hypothenar muscles; Thr Ms, thenar muscles.

  • Fig. 3 Showing distal part of the AcMTn (right limb), lying lateral to FDPTn. Bipennate 1st LB taking origin from tendon of FDP and tendon of accessory muscle, passing lateral to these tendons to the dorsum of the hand. AcMTn, accessory muscle tendon; FDPTn, tendon of the Flexor Digitorum Profundus; 1st LB, first lumbrical; DTs, digital tendons; Thr Ms, thenar muscles; ADP, adductor pollicis; HThr Ms, hypothenar muscles; LB, other lumbricals; Br-MN, branch of median nerve.



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