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Fig. 2. Schematic representation of the longitudinal deformation of the tongue body
and the interaction with the tongue ensheathing. The extrinsic muscles are
only partly drawn. Abbreviations: dsh, distal tongue ensheathing; ggl, m.
genioglossus; hgl, m. hyoglossus; psh, proximal tongue ensheathing; sh, tongue
sheet. (A) Detail from Fig. 1A.
The tongue sheet is a tubular structure that inserts the tongue body at the
proximal and distal ensheathing, thus forming a loose second `skin' around the
tongue body. (B) In the retracted `rest' position, the tubular sheet distally
folds inward, resulting in a double sheathing along the tongue tip. The outer
layer of the tongue sheet is fixed to the connective tissue of the mouth floor
(as indicated by the thin vertical lines). (C) While the tongue protrudes, the
inner sheet unfolds outward as the posterior tongue part, i.e. between the
proximal and distal ensheathing, elongates and the distal tongue part is
revealed. Thus, the tongue sheet forms an almost frictionless bearing for
tongue protrusion.
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