part of part of in taxon has muscle origin has muscle origin has muscle insertion has muscle insertion has muscle antagonist Homo sapiens radius bone forelimb zeugopod extensor pollicis longus muscle forelimb zeugopod muscle proximal epiphysis of distal phalanx of manual digit 1 flexor pollicis longus muscle http://upload.wikimedia.org/wikipedia/commons/7/72/FPL.png Wikipedia:Flexor_pollicis_longus_muscle flexor pollicis flexor pollicis longus UBERON:0008446 flexor pollicis muscle SCTID:361818001 A muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. Modern humans are unique among hominids in having a flexor pollicis longus (FPL) muscle belly that is separate from that of the flexor digitorum profundus (FDP). While the FPL is not a separate muscle belly in extant great apes, a distinct tendon from the FDP belly might be present. In some individuals this tendon tend to act more like a ligament which restricts extension of the interphalangeal joint of the thumb. In orangutans there is a tendon similar in insertion and function to the FPL in humans, but which has an intrinsic origin on the oblique head of the adductor pollicis musculus flexor pollicis longus FMA:38481