

TYMPANIC CAVITY 



forward, forming in its course a slight curve the convexity of which is upward and 

 backward. Its inner end is smaller than the outer, and sloped, the anterior wall 

 projecting beyond the posterior for about 4 mm.; it is marked, except at its upper 

 part, by a narrow groove, the tympanic sulcus, in which the circumference of the 

 tympanic membrane is attached. Its outer end is dilated and rough in the greater 

 part of its circumference, for the attachment of the cartilage of the auricula. The 

 front and lower parts of the osseous portion are formed by a curved plate of bone, 

 the tympanic part of the temporal, which, in the fetus, exists as a separate ring 

 (annulus tympanicus,) incomplete at its upper part (page 146). 



Auditory tube 



Condyle of mandible 



Internal carotid 

 artery 



Internal acoustic 

 meatus 



Part of parotid gland 

 Tragus 



External acoustic 

 meatus 



Tympanic cavity 

 Tympanic membrane / 



Mastoid air-cetts 



Transverse sinus 



Helix 



FIG. 90S. Horizontal section through left ear; upper half of section. 



ie skin lining the meatus is very thin; adheres closely to the cartilaginous 

 and osseous portions of the tube, and covers the outer surface of the tympanic 

 membrane. After maceration, the thin pouch of epidermis, when withdrawn, 

 preserves the form of the meatus. In the thick subcutaneous tissue of the cartil- 

 aginous part of the meatus are numerous ceruminous glands, which secrete the 

 ear-wax; their structure resembles that of the sudoriferous glands. 



Relations of the Meatus. In front of the osseous part is the condyle of the mandible, which 

 however, is frequently separated from the cartilaginous part by a portion of the parotid gland. 

 The movements of the jaw influence to some extent the lumen of this latter portion. Behind the 

 osseous part are the mastoid air cells, separated from the meatus by a thin layer of bone. 



The arteries supplying the meatus are branches from the posterior auricular, internal maxillary, 

 and temporal. 



The nerves are chiefly derived from the auriculotemporal branch of the mandibular nerve 

 and the auricular branch of the vagus. 



The Middle Ear or Tympanic Cavity (Cavum Tympani; Drum; 



Tympanum). 



The middle ear or tympanic cavity is an irregular, laterally compressed space 

 within the temporal bone. It is filled with air, which is conveyed to it from the 

 nasal part of the pharynx through the auditory tube. It contains a chain of mov- 

 able bones, which connect its lateral to its medial wall, and serve to convey the 

 vibrations communicated to the tympanic membrane across the cavity to the 

 internal ear. 



