Antagonistic longitudinal divaricator muscle fibers are believed to straighten or shorten the tongues (Karling, 1961; Rieger et at, 1991).
The symmetrical hook supports contain radial myofilament bundles (or longitudinal muscle rows; see below) and lateral divaricator muscle fibers (or external longitudinal, or hook, abductor muscle fibers) that generate hook movement (Doe, 1976).
3B) of transverse sections below the hooks show that each hook support is composed of (A) lateral divaricator muscle fibers, (B) a glandule-muscular core surrounded by an electron-dense matrix that is continuous with the hook inner wall, and (C) a medial glandular region.
The longitudinal, lateral divaricator muscle fibers are the only other muscle group in the hook supports (Figs.
3) in the area where the radial myofilament bundles, the divaricator muscle fibers, and the retractor muscles are connected at the base of the proboscis.
As Doe (1976) noted, the hook support, including the divaricator muscle fibers, the glandulo-muscular core, and the medial glandular area are all surrounded by a basement membrane.
Karling (1961) and Schilke (1969) suggested that lateral divaricator muscle fibers contract to rotate the hook tips open while the radial myofilament bundles contract to provide skeletal support and resist the compressional forces exerted by the divaricator muscles (Fig.