376 MUSCLES. 



the arytenoid cartilages against it, so that the opening of the 

 glottis is protected.* 



The Omo-Hyoideus, 



Passes obliquely across the neck, from the superior edge of 

 the scapula to the os hyoides. It is a thin, narrow muscle, di- 

 vided into two bellies, one at each end, by an intermediate ten- 

 don; its inferior part is concealed by the trapezius muscle; its 

 middle, where the tendon exists, crosses the great vessels of the 

 neck, and is covered by the slerno-eleido-mastoid muscle; and 

 its upper extremity is overlapped by the platysma myodes. 



It arises from the scapula just behind the notch in its supe- 

 rior costa, and curving somewhat downwards in its course, it is 

 inserted into the lower edge of the base of the os hyoides, next 

 to its cornu. 



It draws the os hyoides downwards.f 



The Digastricus, 



Is placed at the upper side of the neck, and passes from the 

 back part of the base of the head to the chin. 



It arises principally fleshy from the fossa of the temporal bone 

 at the base of the mastoid process; its middle is converted into 

 a round tendonj which passes through the stylo-hyoideus mus- 

 cle, and is fixed by a ligamentous loop to the cornu of the os 

 hyoides. After which another fleshy belly is formed, which is 

 inserted into the inside of the base of the maxilla inferior, at 

 the side of its symphysis. It receives an accession from the 

 base of the os hyoides. 



Its use is to draw the os hyoides upwards when its extremi- 

 ties are fixed, and, as Mr. Hunter has pointed out, to throw the 

 head backwards, and thereby to open the mouth when the lower 

 jaw is fixed upon a body of the same height.J 



* Varieties. Its fibres sometimes run into those of the middle constrictor of 

 the pharynx; sometimes they arise from the cricoid cartilage; sometimes it is 

 continuous with the sterno-thyroideus. 



t Varieties. Sometimes it is double, so that besides the usual insertion, it has 

 one into the side of the tongue. 



t A common variety in this muscle consists in the mutual adhesion of the 

 two anterior bellies belonging to the opposite sides, showing thereby a marked 

 tendency to the quadruped arrangement. 



