ORGANS OF SPECIAL SENSE. 363 



and tympanum. Its pharyngeal orifice is trumpet-shaped, and 

 opens at the side of the pharynx, behind the inferior meatus. 



Muscles of the Eustachian tube: 



Tensor palati (tensor veil), the most important has been 

 described (ride Palatal legion). Its action is to pull the ante- 

 rior wall of the tube outward and downward, and widen the canal. 



Internal Pterygoid (vide Muscles). Some fibres are in- 

 serted into the floor of the tube. It acts as tensor of the fascia. 



Ligamenta sal ping o-pliaryngeal, arises from the superior and 

 middle constrictors of the pharynx, and is inserted by three to 

 five tendinous cords into the pharyngeal orifice of the tube. 

 Action, opens the tube. 



Arteries of Eustachian Tube. Pharyngeal from the ex- 

 ternal carotid, middle meningeal from the internal maxillary, 

 and small branches from the internal carotid. 



Nerves, by branches from the glosso-pharyngeal, inferior 

 maxillary, otic ganglion, and facial nerve. 



M K.Mi'.HAXA TYMPANI is a thin, parchment-like membrane, 

 stretched upon the annulus tympanicus, forming the bottom of 

 the external auditory canal, and separating it from the tym- 

 panum. It is placed obliquely downward and inward at an angle 

 of 45. 



Structure. Its three layers are : 



External or cuticular, derived from the skin of the meatus ; 



Middle or fibrous, consisting of two sets of fibres, radiating 

 and circular, the latter forming a tendinous ring around the 

 margin; 



Internal or raucous, continuous with the mucous membrane 

 of the tympanum. 



Its outer surface presents : 



Manubrium of malleus, projecting downward and backward ; 



Processus gracilis of malleus, projecting outward above the 

 manubrium ; 



Umbo, a depression of the membrane formed by the lower 

 end of the manubrium ; 



Yellow spot, the cartilaginous end of the manubrium ; pyra- 

 mid of H<jlit, a triangular cone of reflected light in the antem- 

 inl'erior < mad rant of the membrane. 



Inner surface (vide Outer Wall of Tympanum). 



Arteries, tympanic branch of inferior, branch from the in- 

 ternal carotid. 



Nerves, from the superficial temporal branch of the trifacial, 

 and from the tympanic plexus. 



