)LE EAR OR TYMPANIC CAVITY 



1043 



with the horizontal plane. It is formed partly of bone, partly of cartilage and fibrous 

 tissue (Figs. 819, 915). 



The osseous portion (pars osseo tubas auditivoe} is about 12 mm. in length. It 

 begins in the carotid wall of the tympanic cavity, below the septum canalis musculo- 

 tubarii, and, gradually narrowing, ends at the angle of junction of the squama and 

 the petrous portion of the temporal bone, its extremity presenting a jagged margin 

 which serves for the attachment of the cartilaginous portion. 



TENSOR TYMPANI 



MEMBRANA 

 TYMPANI 



_PHARYNGEAL OPEN 

 NG OF TUBE 



FIG. 915. Auditory tube, laid open by a cut in its long axis. (Testut.) 



The cartilaginous portion (pars cartilaginea tubae auditivce), about 24 mm. in length, 

 is formed of a triangular plate of elastic fibrocartilage, the apex of which is attached 

 to the margin of the medial end of the osseous portion of the tube, while its base 

 lies directly under the mucous membrane of the nasal part of the pharynx, where 

 it forms an elevation, the torus tubarius or cushion, behind the pharyngeal orifice of 

 the tube. The upper edge of the cartilage is curled upon itself, being bent laterally 

 so as to present on transverse section the appearance of a hook; a groove or furrow 

 is thus produced, which is open below and laterally, and this part of the canal is 

 completed by fibrous membrane. The cartilage lies in a groove between the petrous 

 part of the temporal and the great wing of the sphenoid; this groove ends opposite 

 the middle of the medial pterygoid plate. The cartilaginous and bony portions of 

 the tube are not in the same plane, the former inclining downward a little more 

 than the latter. The diameter of the tube is not uniform throughout, being greatest 

 at the pharyngeal orifice, least at the junction of the bony and cartilaginous por- 

 tions, and again increased toward the tympanic cavity; the narrowest part of the 

 tube is termed the isthmus. The position and relations of the pharyngeal orifice 

 are described with the nasal part of the pharynx. The mucous membrane of the 

 tube is continuous in front with that of the nasal part of the pharynx, and behind 

 with that of the tympanic cavity; it is covered with ciliated epithelium and is thin 

 in the osseous portion, while in the cartilaginous portion it contains many mucous 

 glands and near the pharyngeal orifice a considerable amount of adenoid tissue, 

 which has been named by Gerlach the tube tonsil. The tube is opened during deglu- 



