282 



MUSCLES OF THE HEAD AND NECK. 



tendon is connected with the body and great cornu of the os hyoides by 

 a broad band of aponeurotic fibres in the form of a loop, and hned with 

 synovial membrane, and by the fleshy fibres of the stylo-hyoid muscle, 

 through which the tendon passes. 



lielntionx. — =Tlae anterior belly, placed immediately beneath the deep cei-vical 

 fascia, rests on the mylo-hyoid muscle ; it is connected with its fellow of the 

 opposite side by dense fascia, and occasionally is imited by muscular fibres to it 

 or to the mylo-hyoid muscle. 



The posterior belly is covered by the mastoid process and the muscles arising 

 from that bone, and crosses the external carotid artery, and the internal jugTilar 

 vein. 



Fig. 208. — View of the Sub- 

 maxillary Muscles and 

 THE Depressors op the 

 Hyoid Bone and Larynx, 

 from before. (a. t. ) ^ 



On the right side, tlie platys- 

 ma alone has been removed ; 

 on the left side both the 

 bellies of the digastric, the 

 stylo-hyoid, the uiylo-hyoid, 

 the stcrno-hj'oid, 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 ; €, x)laced on the front of 

 the thyroid cartilage, points 

 to the thyro-hyoid muscle ; /, 

 upper part of the sternum ; 

 'J, lateral lobe, and + , isth- 

 mus of the thyroid gland ; 

 above + , the front of the 

 cricoid cartilage covered by 

 the crico-thjToid 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 tlie right side ; 6, stylo-hyoid of the right side ; 7, stylo-pharyngeus of the 

 left side ; 8, placed on tlie levator scapulaa, 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 orao-hyoid. 



Varieties. — The digastric muscle is subject to many variations. The posterior 

 belly may receive an accessory slip from the styloid process (Wood), or from 

 the angle of the lower jaw (Henle). It has been seen arising from the styloid 

 Ijrocess. Rarely the muscle is monogastric. the posterior belly alone being present 

 and being inserted into the ramus of the jaw (]Mc"\\liinnie). The anterior belly 

 is frequently divided into two or more parts, one or even two of which may cross 

 the middle line and decussate -with similar slips from the muscle of the opposite 

 side : or a slip sometimes passes to the median raphe of the mylo-hyoid, with 

 which and its fellow of the opposite side it becomes incorporated. The tendon 

 of the digastric has been seen in front of, or more rarely behind the stylo-hyoid 

 instead of passing through it. 



The mcnto-lnjoid (Macalister) is an occasional mesial slip found passing 



