MYL 0-H } OW—GENIO-HYOID 451 



Origin. — The whole lengtli of the mylo-liyoid ridge on the inner surface of the 

 body of the mandible. 



Insertion. — (1) The lower edge of the anterior surface of the body of the hyoid 

 bone; (2) a median raphe extending from the middle of the loAver border of the 

 body of the hyoid bone to the back of the symphysis of the mandible innnediately 

 below the genial tubercles. 



Structure. — Arising l)y fleshy and short tendinous fibres intermingled, the 

 muscle passes inwards and slightly downwards to its insertion by short tendinous 

 fibres into the median ra])he and hyoid bone. Sometimes the fleshy fibres are here 

 and there continuous with those of the other side. Each of them is somewhat 

 arched, so that the whole sheet has a slight downward convexity. The muscles of 

 the two sides together form a curved diaphragm which stretches across the angle 

 containofl Ix^tween the two portions of the mandil)le. 



Nerve-supply. — From the third (or mandibular) division of the fifth cranial 

 nerve, by the mylo-hyoid branch of the inferior dental which enters the nnder 

 surface of the muscle by several filaments. 



Action. — (1) To raise the tongue, the floor of the mouth, and the hyoid bone, as 

 in mastication and the first part of swallowing. By its elevation of the hyoid bone 

 it will also exert some influence on the larynx and lower part of the pharynx. 

 These actions will be most efficiently carried out when the jaw is closed. (2) 

 Acting from below, it will help in the depression of the lower jaw and in opening 

 the mouth. 



Relations. — Upon its under surface lie the superficial portion of the submax- 

 illary gland, the submental artery, and the anterior belly of the digastric muscle. 

 Above, it is in contact with the genio-hyoid and hyo-glossus, the sublingual 

 gland, the deep portion of the submaxillary gland, and the hypoglossal nerve. 



Variations. — The mylo-hyoid may be closely connected with the anterior belly of the diga.«tric. 

 Openings are sometimes found in the muscular sheet, containing lobules of the submaxillary 

 gland. 



4. GENIO-HYOID 



The genio-hyoid — named from its attachment to the chin (yi'^sur/) and the 

 hyoid bone — is somewhat fusiform, but flattened from above downwards behind, 

 and from side to side in front. 



Origin. — The lower genial tubercle. 



Insertion. — The anterior surface of the body of the hyoid bone. 



Structure. — Arising by a short tendon, its fibres pass backwards and slightly 

 downwards, close to those of the corresponding muscle of the other side. Near 

 the hyoid bone they spread out laterally, and occupy nearly the whole of the 

 upper and anterior surface of the body, sometimes even a small ])ortion of the 

 greater cornu. 



Nerve-supply. — The hypoglossal nerve, which sends filaments to the deep 

 surface. 



Action. — (1) To raise and draw forwards the hyoid bone; (2) to draw down the 

 mandible. In its direction and action it is closely related to the anterior belly of 

 the digastric. 



Relations. — Superficially, the mylo-hyoid muscle; deeply, the genio-hyo- 

 glossus; on its median surface, the corresponding muscle of the other side. 



Variations.— The genio-hyoid may be double, or it may form one muscle witli its fellow of 

 the opposite side. 



THE EXTRINSIC MUSCLES OF THE TONGUE 



The tongue consists chiefly of muscular tissue, part of which arises from the 

 adjacent bones, Avhile the rest is made up of bands of fibre which pass in various 

 directions in its substance, and have no external attachment. The latter or intrinsic 



