184 DIGESTION. 



The isthmus of the fauces, or the strait through which the 

 food passes from the mouth to the pharynx, is thus bounded 

 above by the soft palate and the uvula ; laterally, by the pil- 

 lars of the palate and the tonsils ; and below, by the base of 

 the tongue. 



The openings into the pharynx above are the posterior 

 nares and orifices of the Eustachian tubes. Below, are the 

 openings of the oesophagus and the larynx. 



The muscles of the pharynx are the superior constrictor, 

 the stylo-pharyngeus, the middle constrictor, and the inferior 

 constrictor ; and it is easy to see, from the situation of these 

 muscles, how, by their successive action from above down- 

 ward, the food is passed into the oesophagus. 



The superior constrictors form the muscular wall of the 

 upper part of the pharynx. Their origin extends from the 

 lower third of the margin of the internal pterygoid plate of 

 the sphenoid bone to the alveolar process of the last molar 

 tooth, the intermediate line of attachment being to tendons 

 and ligaments. The fibres then pass backward and meet in 

 the median raphe, which is attached by apeneurotic fibres 

 to a ridge on the basilar process of the occipital bone, called 

 the pharyngeal spine. 



The stylo-pharyngeus muscle has a rounded portion 

 above by which it arises from the inner surface of the base of 

 the styloid process of the temporal bone. It passes between 

 the superior and middle constrictors of the pharynx, becomes 

 thin, and spreading out, its fibres mingle in part with the 

 fibres of the constrictors and the palato-pharyngeus, and a few 

 pass to be inserted into the upper border of the thyroid carti- 

 lage. 



The middle constrictor is a flattened muscle arising from 

 the cornua of the hyoid bone and the stylo-hyoid ligament ; 

 its fibres passing backward, spreading into a fan shape, and 

 meeting in the median raphe. 



The inferior constrictor is the most powerful of the mus- 

 cles of the pharynx. It arises by thick fleshy masses from 



