ORGANS OF SPECIAL SENSE. 361 



and occipitalis minor; auricularis magnus, from the cervical 

 plexus; and posterior auricular, from the facial. 



AUDITORY CANAL, or meatus auditorius externus, is an osseo- 

 cartilaginous canal, about one and one-fourth inches in length, 

 extending from the concha to the tympanic membrane. 



The osseous portion forms about two-thirds of the passage, 

 and consists in greater part (anterior and lower) of a curved 

 plate of bone the annulus tympanicus. 



The anterior and upper part of the ring present two spines 

 spina tympanica, major and minor, for the ligaments of the 

 malleus. 



The sulcus tympanicus is a furrow on the inner edge of the 

 ring, for the attachment of the tympanic membrane. 



The cartilaginous portion forms about one-third of the pas- 

 sage, and consists of the inverted cartilage of the tragus and 

 concha, the upper and back part of which is deficient, the cleft 

 being filled with fibrous tissue. 



The canal, including the tympanic membrane, is lined 

 throughout with skin, containing short hairs, vascular papilla?, 

 sebaceous and ceruminous glands. 



Arteries branches of the internal maxillary, posterior 

 auricular, and temporal branches of external carotid. 



Nerves from the auriculo-temporal branch, the inferior 

 maxillary, and auricular branch of the pneumogastric. 



MIDDLE EAR, OR TYMPANUM, 



is an irregular cavity, situated between the auditory canal and 

 the labyrinth, communicating with the pharynx through the 

 Eustachian tube, and also with the mastoid cells. It contains 

 a chain of movable bones, part of the chorda tympani nerve, and 

 is filled with air. Its average diameters are about half an inch 

 in height and width, and a line or two in depth from without 

 inward. It is lined with mucous membrane, continuous with 

 that of the Eustachian tube and mastoid cells, and which is 

 reflected over all the tympanic contents. It is bounded by a 

 roof, floor, and four walls, which present the following points : 



Roof, a very thin plate of bone, separates the tympanum 

 from the cranial cavity, and corresponds to a depression on the 

 anterior wall of the petrous bone ; 



Floor, forms the bottom of the jugular fossa, and pre- 

 sents : 



The opening for Jaeolxoris nerve, the tympanic branch of the 

 glosso-pharyngeal. 



