OMO-HYOIDEUS ELEVATORS OF THE OS HYOIDES. 161 



and is inserted into the lower border of the body and great cornu of 

 the os hyoides. 



Relations. By its external surface with the sterno-hyoid and omo- 

 hyoid muscle ; by its internal surface with the great ala of the thy- 

 roid cartilage, the thyro-hyoidean membrane and the superior laryn- 

 geal artery and nerve. 



The omo-hyoideus (u^os, shoulder) is a double-bellied muscle pass- 

 ing obliquely across the neck from the scapula to the os hyoides; it 

 forms an obtuse angle behind the sterno-mastoid muscle, by means 

 of a process of the deep cervical fascia which is connected to the 

 inner border of its tendon. It arises from the upper border of the 

 scapula, and from the transverse ligament of the supra-scapular 

 notch, and is inserted into the lower border of the body of the os 

 hyoides. 



Relations. By its superficial surface with the trapezius, the sub- 

 clavius and clavicle, the deep cervical fascia and platysma myoides, 

 the sterno-mastoid, and the integument. By its deep surface with 

 the brachial plexus, the scaleni muscles, the phrenic nerve, the sheath 

 of the common carotid artery and jugular vein, the descendens noni 

 nerve, and the sterno-thyroid, and thyro-hyoid muscle. The scapu- 

 lar portion of the muscle divides the great posterior triangle into a 

 superior or occipital triangle ; and an inferior or subclavian triangle, 

 which contains the subclavian artery and brachial plexus of nerves ; 

 the other two boundaries of the latter being the sterno-mastoid in 

 front and the clavicle below. The hyoid portion of the muscle, 

 divides the great anterior triangle into an inferior carotid triangle 

 situated below the muscle, and into a superior triangle which lies 

 above the muscle and is again subdivided by the digastricus muscle 

 into the submaxillary triangle and the superior carotid triangle. The 

 other two boundaries of the inferior carotid triangle, are the middle 

 line of the neck in front and the anterior border of the sterno-mas- 

 toid behind. The other boundaries of the superior carotid triangle 

 are the posterior belly of the digastricus muscle above and the an- 

 terior border of the sterno-mastoid behind. 



Actions. The four muscles of this group are the depressors of 

 the os hyoides and larynx. The three former drawing these parts 

 downwards in the middle line, and the two omo-hyoidei regulating 

 their traction to the one or other side of the neck, according to the 

 position of the head. The omo-hyoid muscles by means of their 

 connexion with the cervical fascia are rendered tensors of that por- 

 tion of the deep cervical fascia which covers in the lower part of 

 the neck, between the two sterno-mastoid muscles. 



Third Group. Elevators of the Os Hyoides. 



Digastricus. 

 Stylo-hyoid, 

 Mylo-hyoid, 

 Genio-hyoid, 

 Genio-hy o-glossus . 

 21 



