title: Development of the deep flexor tendons and lumbricalis muscle in the hand and foot: a histological study using human mid-term foetuses.
abstract: To revisit foetal development of the deep flexor tendons of the hand and  foot, we examined the paraffin-embedded histology of 20 mid-term foetuses  at 8-15 weeks of estimated gestational age (35-118 mm crown-rump  length or CRL). At 8-9 weeks, in front of the metacarpal bones, the flexor  pollicis longus and flexor digitorum profundus (FDP) muscles provided  a plate-like, common tendon from which the lumbricalis muscles originated.  However, in the foot, we had no evidence of such a common tendon. The  flexor pollicis tendon was separated from the common tendon at 9-10 weeks  possibly due to mechanical stress from the laterally growing thumb. Notably,  at the lumbricalis muscle origins at 10-12 weeks, the FDP and flexor  digitorum longus tendons remained undifferentiated and the primitive tenocytes  were dispersed from them. The dispersed cells seemed to develop into  an interface tissue between the lumbricalis muscle fibre and the deep tendon.  In 3 of 5 specimens at 15 weeks, we found an excess number of the  FDP tendons (5-7) in the proximal side of the lumbricalis muscle origin.  However, the excess tendons dispersed in the lumbricalis muscle origin. The  development of the lumbricalis muscle origin might follow the tendon splitting  for four fingers. However, conversely, we hypothesised that the developing  lumbricalis muscles re-arranged the deep flexor tendons to provide  a configuration of one deep tendon per one finger (or toe). The quadrates  plantae muscle seemed not to contribute on the re-arrangement.
authors.affiliation: Department of Neurology, Wonkwang University School of Medicine and Hospital, Iksan, Korea. neurlogy@wonkwang.ac.kr
authors.forename: K H
authors.initials: KH
authors.lastname: Cho
authors.forename: J H
authors.initials: JH
authors.lastname: Kim
authors.forename: Y S
authors.initials: YS
authors.lastname: Ha
authors.forename: G
authors.initials: G
authors.lastname: Murakami
authors.forename: B H
authors.initials: BH
authors.lastname: Cho
authors.forename: S
authors.initials: S
authors.lastname: Abe
mesh_terms: D005260:Female; D005333:Fetus / Q000166:cytology / Q000196:embryology; D005865:Gestational Age; D006801:Humans; D008297:Male; D050279:Metacarpal Bones / Q000166:cytology / Q000196:embryology; D024510:Muscle Development / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000196:embryology; D013710:Tendons / Q000166:cytology / Q000196:embryology; D013933:Thumb / Q000033:anatomy & histology / Q000196:embryology