ANATOMY AND PHYSIOLOGY 



19 



G. The Sense Organs and the Nervous System 



Exercise 17. — The Ear. 



(a) In order to remove the skin from the ear make a V-shaped 

 incision in the skin, with the point just in front of the ear and the 

 sides of the V passing above and below it. Hold the skin at the point 

 of the V with forceps, slowly pull it backwards, and expose a circular 

 area still covered with the delicate tympanic membrane which is 

 thickened at its center. Cut through this membrane, avoiding the 

 thickened center, and thus lay open the cavity of the middle ear 

 which connects with the mouth cavity by way of the Eustachian tube 

 (Fig. 19). What is the function of the Eustachian tube? Demon- 



semlcircula/ 



ejfterrra/ ear* 



o<jc//toru 



auditor(/ cana/ 



;-> cocA/ea 



^ £as tach/'an 

 tube 



phar(//7x 



Fig. 19. — The human ear; diagrammatic. The cavity of the middle ear con- 

 tains the ear-bones that transmit vibrations from the tympanic membrane to 

 the inner ear and is connected by the Eustachian tube with the pharynx. 



(From T. Hough and W. T. Sedg^vick, "Human Mechanism," copyright, 1918, by Ginn 

 and Co., reprinted by permission.) 



strate its relation to the eardrum in the human body by holding your 

 nose, closing your mouth, and exhaling. Notice the columella of the 

 frog's ear, a slender bone extending upward and inward from the 

 thickened center of the tympanic membrane to the skull. The func- 

 tion of the columella is to transmit sound waves across the cavity of 

 the middle ear from the tympanic membrane to the nerve endings of 

 the inner ear. The inner ear is embedded in the bone of the skull 

 and is difficult to dissect. Understand its structure from demonstra- 

 tions. A model of the human ear and dissection of a shark's inner 

 ear should be examined if available. 



