SUPEA-HYOID MUSCLES. 



from the body of tlie 03 hyoides to the chin. It sonaetimes consists of two 

 parallel bands, and Macalister suggests that it may be a differentiated portion of 

 the platysma. 



The stylo-hyoid muscle lies close to the posterior belly of the 

 digastric muscle, being a little behind and beneath it. It arises from 

 the outside of the middle of the styloid process of the temporal bone, 

 and inclines downwards and forwards, to be inserted into the os hyoides 

 at the union of the great cornu with the body. Its fibres are usually 

 divided into two fasciculi near its insertion, for the transmission of the 

 tendon of the digastric muscle. 



Eehrtioiu^. — The upper part of the stylo-hyoid muscle lies deeply, being covered 

 by the stemo-mastoid and digastric muscles, and by part of the parotid gland ; 

 the middle crosses the external carotid artery ; the insertion is comparatively 

 superficial. 



Varieties. — This muscle is sometimes wanting ; occasionally a second is present 

 (stylo-hyoideus alter, — Alb.) The position too may be varied — it has been found to 

 the inner side of the external cai'otid ai-teiy instead of over that vessel. (" The 

 Anatomy and Operative Sm-geiy of the Arteries," by E. Quain, plate 12, fig. 5. 

 Macalister, Journal of Anat., vol. v., p. 28.) 



The mylo-hyoid muscle arises from the mylo-hyoid ridge along the 

 inner surface of the lower jaw, extending from the last molar tooth to 

 the symphysis. The posterior fibres are inserted into the body of the 



Fig. 209. 



Fig. 209. — A, THE Lower Jaw and Hyoid 

 Bone, from below, with the ilYLO-HYOiD 

 Muscles attached. 



b, the same from behind, with the mylo- 

 HYOID AND GeNIO-HyoIJ) MuSCLES ATTACHED. 



(A.T.) 1' 



Of, the symphysis ; h, the angle of the lower 

 jaw ; c, the lower border of the body of the 

 hyoid bone ; d, in B, the inferior dental fora- 

 men and upper end of the mylo-hyoid ridge ; 

 1, 1', the mylo-hyoid muscles ; 2, 2', the 

 genio-hyoid muscles from above ; 3, the cut 

 ends of the attiiclunent of the genio-glossi 

 muscles to the su^^erior genial spines. 



OS hyoides ; the rest, proceeding 



parallel to the fibres behind, and 



becoming gradually shorter, join at 



an angle with those of the coitcs- 



ponding muscle, forming with them 



a sort of raphe along the middle 



line, from the symphysis of the jaw 



to the OS hyoides. Thus the two 



muscles together form a floor below the anterior part of the mouth 



\diaj)hragma oris of Meyer). 



Belations. — The lower surface of the mylo-hyoid muscle is covered by the 

 digastric muscle, the submaxillary gland, and the submental vessels and nerve. 

 The deep surface which looks upwards and inwards, is in contact with the genio- 

 hyoideus and part of the hyo-glossus and stylo-glossus muscles, the ninth and 

 gustatory nerves, the sublingual gland, and the duct of the submaxillary gland. 

 Tlie posterior border alone is free and unattached, and behind it the duct of the 

 submaxillary gland turns, in passing to the mouth. 



