194 



SENSE OF HEARING. 



and an invariable accompaniment of the membrana tympani, in animals. 



Without the tube, the mem- 

 brane would be almost devoid 

 of function. Pathology shows 

 us, in the clearest manner, 

 that its integrity is necessary 

 to audition ; and that deaf- 

 ness is the consequence of 

 its closure. Dr. Bostock 1 

 thinks, "it is perhaps not 

 very easy to ascertain in 

 what mode it acts, but it may 

 be concluded that the proper 

 vibration of the membrana 

 tympani is, in some way, 

 connected with the state of 

 the air in the tube." The 

 name of the cavity to which 

 the tube forms a communi- 

 cation with the external air 

 suggests an easy and sufficient 

 explanation of its use. The 



Vertical Section of the Head and Neck through the drum of the ear, like every 



Mesial Line, to show the opening of the Eustachian drum, requires an aperture 

 Tube and its relations ' th ^ Pha^m-.- . - . 



in some part of its parietes, 



1. Section of the os frontis. 2. Section of the os occipi- i ,1 , , r 



tis. 3. Muscles on the back of the neck. 4. Integuments "* Order tliat its membranes 



onthechin. 5. Frontal sinus. 6. Middle spongy bone. 7. rnov vilirofp -fYpAlv TVia 



Inferior spongy bone. 8. Middle meatus of the nose. 9. ^^J \10raiC ir ,6iy. J.IH 



Inferior meatus of the nose. 10. Thickness of the roof of Eustachian tube SCrVCS this 

 the mouth and floor of the nostril. 11. Opening of the Eus- j ., 



tachian tube. A catheter is introduced in the nostril and purpose, and its ClOSUre prO- 



about to enter the tube. 12. Cartilaginous nasal septum, J llppa *}, ~xrn(* oflf^f nrnn 



13. Genio-glossus muscle. 14. Soft palate. QUCCS tne Same CffCCt Upon 



the membrana tympani at 



one end of the cylinder, and on the membrane of the foramen ovale at 

 the other, as would be produced on the parchments of the ordinary 

 drum by the closure of its lateral aperture. We can, in this way, 

 account for the temporary deafness, which accompanies severe cases of 

 inflammation of the throat : the swelling obstructs the Eustachian 

 tube. Dr. Carpenter, 2 however, thinks that the effect of the hole in 

 the side of a drum seems rather to be the communication of the sono- 

 rous vibrations of the contained air to the ear of the observer, which 

 are thus transmitted directly through the atmosphere, instead of being 

 weakened by transmission through the walls of the instrument ; and 

 hence he concludes, that there is no real analogy between the two cases. 

 During the constant efforts of deglutition the air is renewed in the 

 cavity of the tympanum ; and, as the extremities of the Eustachian 

 tube terminate in the pharynx, it enters at a modified temperature. 

 The writer last cited thinks the principal object of the tube seems to 

 be maintenance of the equilibrium between the air within the tympanum 



Physiology, 3d edit., p. 721, London, 1836. 

 Human Physiology, 357, London, 1842. 



