=Pterygoideus Externus.= (Synonym.—Pterygoideus lateralis.) _Location._—Supero-external to the pterygoideus internus. _Origin._—From the outer part of the extremity of the orbital process of the quadrate. _Insertion._—The fibers pass downward, outward and forward and are inserted to the inner part of the mandibular ramus. _Shape._—A small round bundle. _Relations._—Inferiorly with the pterygoideus internus. Externally with the inferior maxilla. _Action._—Aids in closing the jaw. =Digastricus= (Fig. 17, No. _B_, 16). _Location._—Extends from the basi-temporal to the side of the neck. _Origin._—From the external lateral angle of the basi-temporal. _Insertion._—Opposite the angle of the jaw the fibers spread out in fan-like arrangement. The muscle meets its fellow of the opposite side; extends longitudinally over the superior larynx, for some distance down the neck. _Shape._—Thin and ribbon-shaped. _Relations._—Externally to the platysma myoides. The anterior fasciculi blend with those of the mylo-hyoideus; internally with the larynx at the upper part. _Action._—To raise the trachea and hyoid apparatus against the pharynx. THE MUSCLES OF THE TONGUE Mylo-hyoideus Stylo-hyoideus Genio-hyoideus Cerato-hyoideus Sterno-hyoideus Depressor-glossus Cerato-glossus Hyoideus transversus =Mylo-hyoideus.= _Location._—The forepart of the inter-ramal space. _Origin._—From the inner side of the lower jaw at a point just above the lower border and the inturned edge of the horny sheath of the beak. _Insertion._—By aponeurosis to the under side of the hyoid, on the median line between the first and the second basi-branchial. _Shape._—Thin, flat, and delicate. _Relations._—Inferiorly with the skin. Thin and rather broad, it meets its fellow of the opposite side. Laterally with the rami of the jaw. Superiorly with the hyoid apparatus. _Action._—Lifts the tongue upward against the roof of the mouth. =Stylo-hyoideus= (Fig. 17, No. _B_, 6). _Location._—Supero-posterior to the hyoid apparatus. _Origin._—From the outer portion of the articular enlargement of the lower jaw. _Insertion._—By a tendon to the basi-branchial of the thyro-hyal. _Shape._—A long transversely flattened fasciculus. _Relations._—Supero-posterior part of the hyoid apparatus along side the genio-hyoideus and the cerato-hyoideus. _Action._—Singly, pulls the tongue to one side; acting with its fellow, pulls the tongue upward. =Genio-hyoideus= (Fig. 9, No. 7). _Location._—Supero-posterior to the hyoid apparatus. _Origin._—From the anterior portion of the inner side of the lower jaw. _Insertion._—To the middle of the outer side of the basi-branchial of the corner of the os hyoides which cornu it completely envelops.