300 



THE MUSCLES OF THE HEAD AND NECK. 



Tel 



arises from the oblique line on the ala of the thyroid cartilage, and is inserted into 

 the lower border of the hyoid bone, extending over the outer half of the body and 

 the anterior half of the great cornu. 



Relations. This muscle is concealed in great part by the sterno-hyoid and omo-hyoid 

 it rests on the ala of the thyroid cartilage, and on the thyro-hyoid membrane. Between that 

 membrane and the muscle, the superior laryngeal nerve and artery are placed before entering 

 the larynx. 



The omo-hyoid is a long ribbon-shaped muscle, consisting of two bellies united 

 by an intervening tendon. It arises from the upper border of the scapula, near 

 the suprascapular notch, and occasionally from the ligament which crosses the 

 notch. Thence it extends forwards and only slightly upwards, across the root of 



Fig. 277. MUSCLES OF THE NECK, FROM 

 BEFORE. (Allen Thomson.) 



On the right side, the platysma alone has. 

 been removed ; on the left side, both bellies- 

 of the digastric, the stylo-hyoid, mylo-hyoid, 

 sterno-hyoid and omo-hyoid muscles have 

 been removed, a, symphysis ; 6, angle of 

 the lower jaw ; c, hyoid bone ; d, mastoid 

 process ; e, placed on the thyroid cartilage, 

 points to the thyro-hyoid muscle ; /, upper 

 part of the sternum ; g, lateral lobe, and + > 

 isthmus of the thyroid body ; above + , the 

 cricoid cartilage and the crico-thyroid mus- 

 cle ; 1, posterioi', and 1', anterior belJy of 

 right digastric muscle ; 2, right mylo-hyoid ; 

 3, left genio-hyoid ; 4, hyo-glossus ; 5, stylo- 

 glossus ; 5', a portion of the same on the 

 right side ; 6, stylo-hyoid of the right side ; 

 7, stylo-pharyngeus of the left side ; 8, placed 

 on the levator scapulae, points to the left 

 middle constrictor of the pharynx ; 9, placed 

 on the middle scalenus, points to the left- 

 inferior constrictor ; 10, right sterno-hyoid ; 



11, placed on the left sterno-thyroid, points, 

 also to the lower part of the right muscle ; 



12, placed on the right sterno-mastoid, points- 

 to the anterior and posterior bellies of the 

 right omo-hyoid. 



the neck, till it passes beneath the sfcerno-mastoid muscle, and then, curving rapidly, 

 it ascends nearly vertically, to be inserted into the lower border of the body of the 

 hyoid bone immediately outside the sterno-hyoid. The tendon which divides the 

 muscle is placed beneath the sterno-mastoid muscle, and varies much in length and 

 form in different bodies. The tendon is enclosed within the deep cervical fascia,, 

 which, after forming a sort of sheath for it, is prolonged downwards, and becomes 

 attached to the sternum and the cartilage of the first rib ; and by this means, as- 

 also by fascia investing the posterior belly and descending to the clavicle, the 

 muscle is maintained in its bent position. 



Relations. At its scapular origin the muscle is covered by the trapezius, in the middle 

 of its course by the sterno-mastoid ; the two bellies appear one in each of the triangles of the 

 neck, the anterior crossing the common carotid artery, the posterior bounding the small 

 triangle in which the subclavian artery is found ; it also lies over the scaleni muscles, the 

 lower cervical nerves, the sheath of the common carotid artery and jugular vein, and the 

 sterno-thyroid and thyro-hyoid muscles. 



Varieties. These are very frequent. The commonest is an attachment to the clavicle,: 

 which may be the sole origin of the posterior belly, or it may be by a supernumerary belly. 

 Complete doubling of the muscle has been observed in a few cases. On the other hand entire 

 absence is recorded ; also absence of the anterior belly, its place being taken by a band of 

 fascia. The anterior belly is sometimes fused with the sterno-hyoid. 



