7H HEARING. [CH. LTII. 



part consists of fibro-cartilage continued from the concha, its 

 inner part of bone. Both are lined by skin continuous with that 

 of the pinna ; the skin also extends over the outer part of the 

 membrana tympani. Towards the outer part of the canal are fine 

 hairs and sebaceous glands, while deeper in the canal are small 



Fig. 536. Diagrammatic view from before of the parts composing the organ of hearing of 

 the left side. The temporal bone of the left side, with the accompanying soft parts, 

 has been detached from the head, and a section has been, carried through it trans- 

 versely; so as to remove the front of the meatus externus, half the tympanic mem- 

 brane, the upper and anterior wall of the tympanum and Eustachian tube. The 

 meatus internus has also been opened, and the bony labyrinth exposed by the removal 

 of the surrounding parts of the petrous bone, i , the pinna and lobe ; 2, meatus 

 externus ; 2', membrana tympani ; 3, cavity of the tympanum ; 3', its opening back- 

 wards into the mastoid cells ; between 3 and 3', the chain of small bones ; 4, Eusta- 

 chian tube ; 5, meatus internus, containing the facial (uppermost) and the auditory 

 nerves ; 6, placed on the vestibule of the labyrinth above the fenestra ovalis ; a, apex 

 of the petrous bone ; 6, internal carotid artery ; c, styloid process ; d, facial nerve 

 issuing from the stylo-mastoid foramen ; e, mastoid process ; /, squamous part of the 

 bone covered by integument, &c. (Arnold.) 



glands, resembling the sweat-glands in structure, which secrete the 

 cerumen or wax of the ear. 



Middle Ear or Tympanum. The middle ear, or tympanum 

 or drum (3, fig. 536), is separated by the membrana tympani horn 

 the external auditory meatus. It is a cavity in the temporal bone, 

 opening through its anterior and inner wall into the Eustachian 

 tube, a cylindriform flattened canal, dilated at both ends, com- 

 posed partly of bone and partly of elastic cartilage, and lined with 

 mucous membrane, , which forms a communication between the 

 tympanum and the pharynx. It opens into the cavity of the 

 pharynx just behind the posterior aperture of the nostrils. 



