THE LARYNX AND THE EAR 369 



large.) The largest represents the thyroid cartilage, the next in size 

 the cricoid, and the two smallest the arytenoid cartilages. By means 

 of pins, or threads, connect these with each other according to the de- 

 scription of the larynx on page 253. With this simple model the move- 

 ments of the different cartilages and their effect upon the vocal cords 

 may be illustrated. 



To show the Relation of the Movements of the Vocal Organs to the 

 Production of Different Sounds. i . Lightly grasp the larynx with the 

 fingers while talking. Observe the changes, both in the position and 

 shape of the larynx, in the production of sounds of different pitch. 

 2. Observe the difference in the action of the muscles of respiration in 

 the production of loud and faint sounds. 3. Pronounce slowly the 

 vowels, A, E, I, O, U, and the consonants C, F, K, M, R, S, T, and 

 V, noting the shape of the mouth, the position of the tongue, and the 

 action of the lips in each case. 



To demonstrate the Ear. Examine a dissectible model of the ear, 

 locating and naming the different parts. Trace as far as possible the 

 path of the sound waves and find the termination of the auditory nerve. 

 Note also the relative size of the parts, and calculate the number of times 

 the model is larger than the natural ear. Suggestion : The greatest 

 diameter of the internal ear is about three fourths of an inch. 



In an extended course it is a profitable exercise to dissect the ear of 

 a sheep or calf, observing the auditory canal, middle ear, bridge of 

 bones, and the tympanic membrane with attached malleus and tensor 

 tympanic muscle. Pass a probe from the nasal pharynx through the 

 Eustachian tube into the middle ear. With bone forceps or a fine saw, 

 split open the petrous portion of the temporal bone and observe the 

 cochlea and the semicircular canals. By a careful dissection other 

 parts of interest may also be shown. 



