MUSCLES OF THE TONGUE (Fig. 96).--=M. genioglossus= (_f_) passes from the symphysis of the lower jaw into the tongue and lies beneath (dorsad of) the geniohyoid (_g_).
_Origin_ from the medial surface of the mandible near the symphysis and dorsad of the origin of the geniohyoid.
_Insertion._--The fibres pass dorsad, diverging in a fan-like manner and forming a flat vertical plate closely applied to the muscle of the opposite side. This plate extends along the caudal three-fourths of the tongue, i.e. as far as it is attached. The cranial fibres arch craniad to the tip of the tongue, the caudal fibres arch caudad to the root of the tongue. Dorsad the muscle is confounded with the muscle of the opposite side.
_Action._--Draws the root of the tongue forward and the tip backward.
=M. hyoglossus= (_h_).--From the body of the hyoid bone to the tongue.
_Origin._--(1) From the ventral surface of the body of the hyoid laterad of the geniohyoid (_g_), and (2) by a second head from the ceratohyal.
_Insertion._--Both heads penetrate into the tongue between the styloglossus (_e_) and the genioglossus (_f_). The fibres intermingle with those of the styloglossus (_e_) and thus help to form the lateral parts of the tongue. They finally end in the integument on the dorsum of the tongue at the sides.
_Action._--Retracts the tongue and depresses it.
=M. styloglossus= (_e_).--From the stylohyal bone to the tongue.
_Origin_ from the mastoid process of the temporal bone, from the stylomandibular ligament (2) (which connects the border of the external auditory meatus with the angular process of the mandible) and from the proximal cartilaginous portion of the cranial cornu of the hyoid bone. The fibres pass mediad, diverging between those of the digastric and hyoglossus (_h_) into the lateral part of the tongue.
_Insertion._--The fibres pass toward the tip of the tongue, where the mass finally ends in a point, the superficial ones gaining insertion into the integument at the sides of the tongue.
_Relations._--Outer surface with the digastric (Fig. 65, _b_) and mylohyoid (Fig. 65, _c_). Inner surface with the pterygoideus internus (Fig. 96, _d_), the cranial cornu of the hyoid, and the tympanic bulla.