1130 



THE ORGANS OF SPECIAL SENSE 



tubae auditivae), the apex of which is attached to the margin of the inner extremity 

 of the osseous canal, while its base lies directly under the mucous membrane of 

 the nasopharynx, where it forms an elevation or cushion above and behind the 

 pharyngeal orifice of the tube. The upper edge of the cartilage is curled upon 

 itself, being bent outward so as to present on transverse section the appearance of 

 a hook (lamina lateralis); a groove or furrow is thus produced, which opens below 

 and externally, and this part of the canal is completed by fibrous membrane. 

 On transverse section the cartilage exhibits the laminae which above are continuous 

 with each other the hard, thick lamina medialis and the thin and hooked lamina 

 lateralis. The cartilage of the Eustachian tube, with a hood plate of cartilage, 

 forms the posterior portion of the inner wall (the lamina medialis). The cartilage 

 is fixed to the base of the skull, and lies in a groove (sulcus tubae auditivae) between 



TENSOR TYMPANI 



MEMBRANA 

 TV M PA N I 



_PHARYNGEAL OPEN- 

 ING OF TUBE 



FIG. 836. Eustachian tube, laid open by a cut in its long axis. (Testut.) 



the petrous portion of the temporal and the greater wing of the sphenoid; this 

 groove ends opposite the middle of the internal pterygoid plate, in a projection, the 

 processus tubarius. The cartilaginous and bony portions of the tube are not 

 in the same plane, the former inclining downward a little more than the latter. 

 They join each other at a large obtuse angle, open below. The diameter of the 

 canal is not uniform throughout, being greatest at the pharyngeal orifice and 

 least at the junction of the bony and cartilaginous portions, where it is named 

 the isthmus (isthmus tubae auditivae); it again expands somewhat as it approaches 

 the tympanic cavity. The position and relations of the pharyngeal orifice are 

 described with the anatomy of the nasopharynx. The mucous membrane of the 

 tube is continuous in front with that of the nasopharynx, and behind with that 

 which lines the tympanum; 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 lymphoid tissue, 

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

 deglutition by the Salpingopharyngeus and Dilatator tubse muscles. 



The Membrana Tympani (Figs. 837 and 838) separates the cavity of the tym- 

 panum from the bottom of the external meatus. It is a thin, semitransparent 



