SCHWENK, K.: Extrinsic vs. intrinsic lingual muscles: the amniote tongue as a functional unit.

The muscular tongue of amniote vertebrates is traditionally described as a composite of two muscle types: extrinsic muscles originate outside the tongue and insert within it; intrinsic muscles arise and insert completely within the tongue. Whole-tongue movements are attributed to the former, lingual shape change to the latter. This dichotomous view of tongue structure and function has endured since the mid-19th century, despite persistent indications of its inadequacy. A histological analysis of the mm. genioglossus and verticalis in mammals and the m. hyoglossus in lepidosaurian reptiles finds: (1) the “extrinsic” m. genioglossus contributes extensively to the “intrinsic” m. verticalis; (2) the verticalis “muscle” is composed of fibers from at least three nominally separate muscles, both extrinsic and intrinsic (genioglossus, longitudinalis inferior, intrinsic verticalis fibers); (3) the “extrinsic” m. hyoglossus in lepidosaurs comprises both extrinsic and intrinsic parts which may be histochemically differentiated. Current models of the tongue as a muscular hydrostat suggest that it functions as an integrated functional unit and that the traditional atomistic, dichotomous view of lingual muscles is inaccurate and misleading. The notion of individuated “muscles” is inapplicable within the tongue and should be replaced by reference to “fiber systems.” This view of the tongue highlights the weakness of an atomistic approach to complex form and calls into question the application of traditional character concepts and character analyses to integrated functional units.