. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 224 Bulletin Museum of Comparative Zoology, Vol. 156, No. 1 its fibers are often shown in sagittal view to end at the base of the tongue before penetrating the medullary core, or to run obliquely across the alternating sheets of vertical and transverse fibers toward the dorsal and posterior surfaces of the tongue (, Kallius, 1910; Abd-El-Malek, 1938; Warwick and Williams, 1973; Crouch, 1978; Walker and Homberger, 1992). In- dependence of the genioglossus from the medullary, intrinsic fiber system is implied in the
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 224 Bulletin Museum of Comparative Zoology, Vol. 156, No. 1 its fibers are often shown in sagittal view to end at the base of the tongue before penetrating the medullary core, or to run obliquely across the alternating sheets of vertical and transverse fibers toward the dorsal and posterior surfaces of the tongue (, Kallius, 1910; Abd-El-Malek, 1938; Warwick and Williams, 1973; Crouch, 1978; Walker and Homberger, 1992). In- dependence of the genioglossus from the medullary, intrinsic fiber system is implied in these and other descriptions. In actu- ality, as genioglossus fibers turn dorsally into the tongue, they become confluent with the serially arranged sheets of verti- calis fibers (Fig. 2A). As such, for most of the tongue's length, the medial portion of the verticalis inuscle comprises genioglos- sus fibers. In other words, a large portion of the "intrinsic" verticalis muscle is com- posed of "extrinsic" fibers. Although the previous observations seem to support the radical position of Cave (1980) and others suggesting that in- trinsic fibers are merely extensions of ex- trinsic muscles, this view is vitiated by a full consideration of m. verticalis anatomy. Although the medial portion of each ver- ticalis sheet comprises extrinsic genioglos- sus fibers, its lateral portion derives from purely intrinsic fibers that originate on the lamina propria of the ventral surface (Fig. 2B). Although medial genioglossus fibers are relatively vertical and lateral intrinsic fibers are oblique (running dorsomedially; see above), fibers of both sorts blend in- sensibly across the breadth of a single ver- ticalis sheet to form a continuous structur- al unit. These units are repeated serially along the length of the tongue, alternating with sheets of m. transversus. Extrinsic and intrinsic components of the verticalis are also clearly evident in the opossum, Monodelphis (Smith,
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