EUSTACHIAN TUBE. 



457 



tympani, when viewed in a microscope, which will magnify 

 twenty-three times, appears to be supplied with muscular fibres 

 arranged in a radiated manner. These fibres are on the inter- 

 nal side of the membrane. He thinks that, under favorable 

 circumstances, they can be seen with the naked eye. 



Fig. 201.* 



CK. 



The Eustachian Tube. 



The communication between the cavity of the tympanum 

 and the fauces is formed by the Eustachian Tube, a canal 



* Fig. 201, represents a vertical section of the auditory apparatus of the left 

 side ; the labyrinth being a little enlarged, in order to render its description 

 more intelligible to the student, a, External ear. b, Lobus of the ear. c, 

 Antitragus. d, Concha, the bottom of which is continuous with the meatus 

 auditorius. e, e, Petrous portion of the temporal bone, in which the auditory 

 apparatus is lodged, e', Mastoid process of the temporal bone, e", Portion of 

 the glenoid cavity of the temporal bone, in which is articulated the condyle of 

 the lower maxillary bone. e n ', Styloid process of the same bone, e"", Ex- 

 tremity of the carotid canal, traversed by the internal carotid artery, before it 

 penetrates into the cavity of the cranium. /, Meatus auditorius externus, g, 

 Membrana tympani. h, Cavity of the tympanum, from which the chain of 



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