This group consists of eight muscles, one of which, the hyoideus transversus, is unpaired. 1. =Mylo-hyoideus.=—This muscle, together with its fellow, forms a sort of sling between the two rami of the lower jaw, in which the tongue is supported. _Origin._—The inner surface of the alveolar border of the mandible. _Insertion._—(1) A median fibrous raphé extending from the symphysis to the hyoid bone; (2) the lingual process and body of the hyoid bone. _Action._—It raises the floor of the mouth, the tongue, and the hyoid bone. _Structure._—Each muscle consists of a thin curved sheet, the fibers passing downward from their origin and then curving toward the median raphé. It is chiefly fleshy, and is thickest behind. The anterior superficial part of the muscle is termed the mylo-glossus. _Relations._—On the superficial surface of the muscles are the ramus, the internal pterygoid and digastricus muscles, and the submaxillary lymph glands. The deep surface is in contact with the mucous membrane of the mouth, the stylo-glossus, hyo-glossus, and genio-hyoideus muscles, the sublingual gland and vessels, the submaxillary duct, and the lingual and hypoglossal nerves. _Blood-supply._—Sublingual artery. _Nerve-supply._—Mylo-hyoid branch of the mandibular nerve. 2. =Stylo-hyoideus.=—This is a slender, fusiform muscle, having a direction nearly parallel to that of the great cornu of the hyoid bone (Fig. 436). _Origin._—The heel-like prominence on the proximal extremity of the great cornu of the hyoid bone. _Insertion._—The anterior part of the thyroid cornu of the hyoid bone. _Action._—It draws the base of the tongue and the larynx upward and backward. _Structure._—It arises by a thin, short tendon, and has a fusiform belly. The tendon of insertion is perforated for the passage of the intermediate tendon of the digastricus, and at this point there is a small synovial sheath. _Relations._—Superficially, the internal pterygoid muscle and the parotid gland; deeply, the guttural pouch, the pharynx, the external carotid and maxillary arteries, and the hypoglossal nerve. _Blood-supply._—External carotid artery. _Nerve-supply._—Facial nerve (stylo-hyoid branch). 3. =Occipito-hyoideus= (M. jugulo-hyoideus; occipito-styloideus).—This is a small triangular muscle, which lies in the space between the paramastoid process and the great cornu of the hyoid bone. _Origin._—The paramastoid (styloid) process of the occipital bone. _Insertion._—The proximal extremity and ventral edge of the great cornu of the hyoid bone. _Action._—It carries the distal extremity of the great cornu backward and upward. Acting with the genio-hyoideus and digastricus, it raises the hyoid bone and the larynx. _Structure._—The muscle is somewhat triangular, its fibers being longer as the ventral border is approached. It blends with the posterior belly of the digastricus. _Relations._—Superficially, the parotid gland; deeply, the guttural pouch.