544 



HUMAN ANATOMY. 



Variations. — The sterno-hyoid may arise entirely from the clavicle or it may extend its origin 

 to the cartilage of the first rib. It is often divided transversely by a tendinous band which may 

 occur either in its lower part on a line with the intermediate tendon of the omo-hyoid or, more 

 rarely, in its upper part on a level with the insertion of the sterno-thyroid. 



2. Omo-Hyoideus (Fig. 541). 



Attachments. — The omo-hyoid is a long, flat muscle consisting of two bellies 

 united by an intermediate tendon. The iyiferior belly arises from the lateral portion 

 of the superior border and the superior transv^erse ligament of the scapula, and is 

 directed forward, medially, and slightly upward to terminate in the intermediate 

 tendon. This lies behind the clavicular portion of the sterno-cleido-mastoid, and is 

 enclosed by the middle layer of the deep cervical fascia, a specially thickened 

 portion of which binds it down to the posterior surface of the clavicle and to the 

 first rib. The superior belly arises at the medial end of the intermediate tendon and 

 passes upward and slighdy medially to be inserted into the lower border of the hyoid 

 bone, lateral to the sterno-hyoid. 



Fig. 541. 



^i^m'^ 



Styloid process 



Stylo-glossus 

 Stylo-pharyngeu: 



Stylo-hyoi 

 Digastric, posterior belly- 

 Rectus capitis anticus major-— 

 Splenius- 

 Sterno-cleido-mastoid 



Levator anguli scapulae 

 Trapezius 



Scalenus anticus 

 Omo-hyoid, 

 posterior belh 



uccmator 



Orbicularis oris 



Depressor anguli 

 Depressor labii 



inferioris 

 Hyo-glossus 



Digastric, anterior belly 

 Mylohyoid 

 H>oid bone 



Inferior pharyngeal constrictor 

 Thyro-hyoid 



hvoid, anterior belly 



Sterno- 

 thyroid 



Muscles of the neck ; lar>-nx has been drawn forward. 



Nerve-Supply. — From the first, second, and third cervical nerves through 

 the ansa hypoglossi. 



Action.— To draw downward the hyoid bone. Acting from above, it will 

 assist slighdy in drawing the scapula upward. This muscle may also act as a 

 tensor of the cervical fascia, thereby preventing undue pressure on the great vessels 

 of the neck. 



Relations. — At its attachment to the scapula the inferior belly is covered by 

 the trapezius and the muscle is crossed in the middle part of its course by the 

 sterno-cleido-mastoid. The inferior belly is in relation posteriorly with the scalene 

 muscles and the roots of the brachial plexus and sometimes with the third portion of 

 the subclavian artery, the transversalis colli and suprascapular arteries, and the supra- 

 scapular nerve. The superior belly crosses the common carotid artery and the 

 internal jugular vein at the level of the cricoid cartilage. 



