THE HYOID BONE MUSCLES 159 



Actions. Either an elevator of the hyoid or depressor of 

 the lower jaw, according to which is fixed; its insertion is not 

 close enough to the hyoid to allow independent action of either 

 belly. 



The Hyoid Bone Muscles 



1. BETWEEN THE BASE OF THE SKULL AND THE HYOID. 

 M. Stylohyoideus. Origin, by narrow tendon from the back 

 of the styloid process near its root: insertion, usually divided 

 for transmission of the digastric tendon, and the two portions 

 pass ununited to the hyoid at the junction of the great cornu 

 and body; almost always a slip ends in the digastric tendon. 



May be wanting, may be double; inserted into the digastric 

 tendon; fibers continued to the omohyoid, thyrohyoid, or 

 mylohyoid muscles. M. stylohyoideus alter (stylochondro- 

 hyoideus or stylohyoideus profundus), from styloid process 

 to the small cornu, accompanying or replacing the stylohyoid 

 ligament. 



II. BETWEEN THE THORAX AND THE HYOID. First Layer. 

 1. M. Sternohyoideus. Origin, posterior surface of manu- 

 brium sterni and sternoclavicular joint, or from joint and 

 clavicle, from clavicle only, sometimes from the first costal 

 cartilage; insertion, inner half of the lower border of the hyoid 

 body. Its inner border approaches its fellow; are far apart 

 below. 



2. M. omohyoidcus, ribbon-shaped, has two bellies and an 

 intermediate tendon. Origin, upper border of the scapula 

 near the notch or from the transverse ligament; passes forward 

 under the trapezius across the scaleni, beneath the sterno- 

 mastoid, then vertically to the lower border of the hyoid, 

 partly beneath and partly in front of the sternohyoid insertion. 

 Its tendon beneath the sternomastoid at the level of the cricoid 

 cartilage is enclosed in the deep cervical fascia, which is pro- 

 longed down to the sternum and first costal cartilage, while 

 the fascia investing its posterior belly descends to the clavicle. 



Second Layer. 1. M. sternothyroideus lies behind the sterno- 

 hyoid, and rises from the posterior surface of the manubrium 

 internal to the sternohyoid, variably from the first and second 

 costal cartilages, diverges from its fellow; inserted into the 

 oblique line of the thyroid cartilage, covering some fibers of 

 the inferior constrictor. 



