|MadSci Network: Anatomy|
That one gave me a pause, as I haven't thought about an aponeurosis in a LONG time.
Our friend Gray -- from where you got the picture -- gives a rather clunky definition at http://www.bartleby.com/107/104.html
A more digestible definition is at http://en.wikipedia.org/wiki/Aponeurosis
How big do they run? Length and width would depend on the muscle. Thickness seems to be about 5 mm, based on http://ard.bmj.com/cgi/content/full/61/10/905 but of course that's thickness per muscle.
P V Balint, D Kane, H Wilson, I B McInnes and R D Sturrock (2002) Ultrasonography of entheseal insertions in the lower limb in spondyloarthropathy Annals of the Rheumatic Diseases 61:905-910
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