Variant third and fourth lumbrical muscles of the left hand

Introduction Most humans have four lumbrical muscles in each hand numbered as first, second, third and fourth from the radial to ulnar side. Lumbrical muscles of the hand flex the second to fifth metacarpophalangeal joints and extend the interphalangeal joints of the fingers [1, 2]. The first and second lumbrical muscles originate from the radial side of the flexor digitorum profundus (FDP) tendons of the second and third fingers, respectively. The third lumbrical muscle originates from the ulnar side of second FDP tendon and radial side of third FDP tendon. Similarly the fourth lumbrical muscle originates from the ulnar side of the third FDP tendon and radial side of fourth FDP muscle tendon [3]. Thus the first and second lumbrical muscles are unipennate, whereas third and fourth are bipennate. Two ulnar and two radial lumbrical muscles are innervated by the ulnar and median nerves, respectively [4]. This paper presents a unique fourth lumbrical muscle in regards to its origin and insertion in the left hand of a 93-yearold male body donor at the University of South Australia Human Anatomy.