[Full Text]. If you log out, you will be required to enter your username and password the next time you visit. The earliest step in chondrogenesis is condensation of the undifferentiated mesenchymal cells into aggregates. Hereditary multiple exostoses of the forearm—also known as hereditary multiple osteochondromas—is another cause of hand and forearm deformity in children and adults.[20]. This page shows some key events of human development during the embryonic period of the first eight weeks (weeks 1 - 8) following fertilization. 1998 May 29. Belonging: Where do I fit in? [Medline]. As the bud grows, the original overlying ectoderm becomes the AER, and both dorsal and ventral polarized mesoderm is recruited for outgrowth. Trends Genet. [4] The development of the chick embryo exhibits this tripartite structure with 3 morphologically discrete digits, making it a popular model of limb development. Like other paired organs (eyes, feet, legs) each hand is dominantly controlled by the opposing brain hemisphere, so that handedness—the preferred hand choice for single-handed activities such as writing with a pencil, reflects individual brain functioning. Polydactyly is the presence of more than the usual number of fingers. In contrast, the capitate, the "keystone" of the distal arch, moves together with the metacarpal bones and the distal arch is therefore rigid. The thumbs of Ardipithecus ramidus, an early hominin, are almost as robust as in humans, so this may be a primitive trait, while the palms of other extant higher primates are elongated to the extent that some of the thumb's original function has been lost (most notably in highly arboreal primates such as the spider monkey). 1996 Jan. 54(1):9-21. J Hand Surg [Am]. The limb bud develops from the Wolff crest and lies opposite the 5 lower cervical and 2 upper thoracic segments. For instance, the proteoglycan Syndecan-3 is highly expressed in prechondrogenic aggregation restricted to the perichondrium and the developing joints (after differentiation). The process of forming separate digits involves the fragmentation of the AER and subsequent apoptosis, which involves programmed cell death (apoptosis) within the digital interspaces. [Medline]. A reliable way of identifying human hands is from the presence of opposable thumbs. They lie in a defined order that corresponds to the topographic and temporal sequence of their expression along the outgrowing upper extremity. The intrinsic muscles of the hand arise from 5 embryonic layers: the interossei dorsalis accessorii, intermetacarpals, flexoris breves profundi, contrahentes, and lumbricals. Last modified: 03/10/2020 - 1:27pm. They are called extrinsic because the muscle belly is located on the forearm. [Medline]. 2015. Gibson-Brown JJ, Agulnik SI, Chapman DL, et al. The fixed and mobile parts of the hand adapt to various everyday tasks by forming bony arches: longitudinal arches (the rays formed by the finger bones and their associated metacarpal bones), transverse arches (formed by the carpal bones and distal ends of the metacarpal bones), and oblique arches (between the thumb and four fingers): Of the longitudinal arches or rays of the hand, that of the thumb is the most mobile (and the least longitudinal). 1996 Aug. 40(4):797-805. 124(7):1355-66. Educational Attainment consists of the adult literacy rate and gross enrollment ratio. Available at http://tiktaalik.uchicago.edu/. Reddi AH. In order to focus on molecular relationships, Montero and Hurle identify a zone beneath the AER and progress zone (PZ) conceptualized as a "distal aggregating region," in which exists a zone of early differentiation and a more proximal region of later differentiation resulting in a segmented digital ray. 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