492 CONSTRICTOR MUSCLES OF THE PHARYNX. 



the superior, middle, and inferior constrictor muscles of the 

 pharynx. 



The fibres of each of these muscles originate on 'each side, 

 and run in an oblique direction to meet in the middle, thus 

 forming the posterior external surface of the dissected pharynx. 



The fibres of the upper muscles originate from the cuneiform 

 processes of the occipital bane, from the pterygoid processes of 

 the os sphenoides, and from the upper and lower jaws, near 

 the last dentes molares, on each side. They unite in a middle 

 line in the back of the pharynx. 



The fibres of the middle muscles originate principally from 

 the lateral parts of the os hyoides, and from the ligaments 

 which connect that bone to the thyroid cartilage. The supe- 

 rior fibres run obliquely upwards, so as to cover a part of the 

 first mentioned muscle, and terminate in the cuneiform process 

 of the occipital bone ; while the other fibres unite with those of 

 the opposite side in the middle line. 



The fibres of the lower muscles arise from the thyroid and 

 the cricoid cartilages, and terminate also in the middle line : 

 those which are superior, running obliquely upwards ; the 

 inferior, nearly in a transverse direction. 



It is obvious, from the origin and insertion of these fibres, 

 that the pharynx must have the power of contracting its 

 dimensions in every respect ; and, particularly, that its diameter 

 may be lessened at any place, and that the whole may be 

 drawn upwards. 



