184 



MUSCLES OF THE HEAD AND NECK. 



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 base of the 

 styloid process of the temporal bone at the external surface ; and from this 

 place it 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. 



The upper part of the stylo-hyoid muscle lies deeply, being covered by the sterno- 

 mastoid and digastric muscles, and by part of the parotid gland ; the middle crosses 

 the carotid arteries ; the insertion is comparatively superficial. 



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 carotoid artery instead of over that vessel. (" The Anatomy and 

 Operative Surgery of the Arteries," by R. Quain, plate 12, fig. 5.) 



Fig. 160. VIEW OF THE SUB- 

 MAXILLARY MUSCLES AND 

 THE DEPRESSORS OP THE 

 HYOID BONE AND LARYNX, 

 FROM BEFORE. ^ 



On the right side, the platys- 

 ma alone has been removed ; 

 on the left side both the 

 bellies of the digastric, the 

 stylo-hyoid, the mylo-hyoid, 

 the sterno-hyoid, and omo- 

 hyoid muscles have been re- 

 moved : a, symphysis ; b, 

 angle of the lower jaw ; c, 

 middle of the body of the 

 hyoid bone ; d, mastoid pro- 

 cess; e, placed on the front of 

 the thyroid cartilage, points 

 to the thyro-hyoid muscle ; f, 

 upper part of the sternum ; 

 {/, lateral lobe, and +, isth- 

 mus of the thyroid gland ; 

 above +, the front of the 

 cricoid cartilage covered by 

 the crico-thyroid muscle ; 1, 

 posterior belly, 1', anterior 

 belly, of right digastric muscle ; 

 2, right mylo-hyoid ; 3, left 

 genio-hyoid ; 4, hyo-glossus ; 

 5, stylo-glossus ; 5', a portion of it seen on 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 upper and lower bellies of the right omo-hyoid. 



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 sym- 

 pliysis. The posterior fibres are inserted into the body of the os hyoides ; 

 the rest, proceeding parallel to the fibres behind, join at an angle with those 

 of the corresponding 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 

 (diaphragma oris of Meyer). 



