TOPOGKAmiCAL ANATOMY OF THE EAR. 161 



of the cartilage, passing forward, inward, and slightly down- 

 ward, and its fibres spread out along the edge of the soft pal- 

 ate and on the side of the pharynx. In contracting, it draws 

 the hook of the cartilage forward and a little downward, thus 

 enlarging the calibre of the tube. The levator palati takes 

 its origin from the temporal bone just below the osseous 

 tube, and passes along the floor of the tube, some of its fibres 

 arising from the lower end of the cartilage ; it is inserted in 

 the uvula, and, in contracting the belly of the muscle which 

 lies along the floor of the tube, becomes thicker : the floor 

 of the tube is raised, and the fibres arising from the cartilage 

 serve to draw the lower end of this away from the opposite 

 wall. 



" The palato-pharyngeus rises from the posterior part of 

 the lower end of the cartilage, passes backward, and is in- 

 serted on the posterior wall of the pharynx. Its action would 

 be to draw the posterior wall of the tube backward ; but, as 

 it is often but slightly developed, it probably only serves to 

 fix the cartilage, so that the other muscles can act more effec- 

 tively. 



" The opening of the tube is thus the result of the action 

 of these three muscles: the tensor-palati, or dilator tubse, 

 draws the hook of the cartilage outward, the cartilage be- 

 comes less curved and the tube is widened ; the levator pa- 

 lati in contracting becomes more horizontal, and draws the 

 lower end of the cartilage inward and upward, thus enlarg- 

 ing the pharyngeal orifice more than 3"'. As soon as these 

 muscles cease acting, the elasticity of the cartilage restores 

 the canal to its former condition." 



It is thus that the action of certain of the muscles of deg- 

 lutition dilates the pharyngeal end of the Eustachian tube. 

 If we close the mouth and nostrils, and make several repeated 

 acts of deglutition, we draw the air from the tympanic cav- 

 ity, and the atmospheric pressure renders the membrane of 

 the tympanum tense, increasing its concavity. By one or 

 two lateral movements of the jaws, we open the tube, the 



