Developmental anatomy of the hand

"The limbs start to develop during 4th week from limb buds which consist of a mass of mesoderm covered by a thick band of ectoderm. At apex of each limb bud ectoderm thickens to form an apical ectodermal ridge. At 6th week, mesoderm in the hand plates has condensed to form digital rays.
Hand and foot are separated from proximal segments by a circular constriction. A second constriction divides proximal portion into arm and forearm or leg and thigh. Mesodermal models of bones are formed during 5th week. Chondrofication centers appear in 5th week (cartilaginous skeleton at 6th week). Osteogenesis of long bones begins in 7th week from primary ossification centers in the middle of the cartilaginous models. Myoblasts of limb buds are derived from myotomes of the somites. Cervical and lumbosacral myotomes form muscles of pectoral and pelvic girdles. Myoblasts aggregate and form a large muscle mass in each limb bud. This muscle mass divides into dorsal (extensor) and ventral (Flexor) components. Originally, limb buds are at right angles with trunk. Flexor aspect ventral and extensor aspect dorsal with pre-axial border cranial and post-axial border caudal. Upper limbs rotate laterally 90o along their longitudinal axes whereas lower limbs rotate medially 90o along longitudinal axes. Synovial joints appear at the beginning of fetal period (9th -10th weeks). Congenital anomalies and functional development will be discussed."

English