On this page is a small short movie of the human upper limb external appearance changes covering the Carnegie stages from 13 to 23. Note the images are not to scale. Notice as the upper limb grows it moves from a lateral appendage to rotate ventrally and bends at the elbow, ending up on the anterior surface of the embryo. (More? see notes on Limb Development).
Quicktime: Arm movie in new window (179 Kb)
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The small movie on this page is to give an overview of the changing external appearance of the upper limb through the Carnegie stages of development.
Limb development requires a study of several systems, a coordinated establishment of pattern on mainly mesodermal components which also have a covering ectoderm (skin) and invading neural (sensory, motor, neural creast) components.
Mesoderm is a fascinationg layer of the trilaminar embryo, unlike ectoderm and endoderm which have an epithelial-like cellular organization, mesoderm layer appears initially to be a disorganised multilayer of cells.
Embryologists historically used the appearance of somites within the mesoderm layer as an accurate "clock" of early embryonic development. Classic chicken staging was by the number of somites present at a particular time. This led to the question of how this "clock" was actually leading to the pattern we observe being generated in the unsegemented presomitic mesoderm (PSM). Today we know some of the signaling processes (Notch and Wnt signaling) 1involved in establishing pattern in the mesoderm.
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CD users can find Quicktime on the CD or the latest version can be downloaded from here Quicktime
Please email Dr Mark Hill if you wish to make a comment about this current project.