322 DISSECTION OF LARYNX. 



trachea. Move this up and down to prove that it is distinct 

 from the thyroid. This is the Cricoid Cartilage. 



8. Observe the sheet of muscle passing from the cricoid to 

 the thyroid. Again move the cricoid toward and from the 

 thyroid ; what does this muscle do ? Cut away this muscle 

 from one side, and see that the cricoid cartilage widens as it 

 passes backward. How are the cricoid and thyroid hinged 

 together ? 



9. Projecting upward and backward from the top of the 

 larynx are two curved yellowish cartilages, the Arytenoid Car- 

 tilages. Move them about to see that they are movable, and 

 that they rest on the upper edge of the back part of the 

 cricoid cartilage. 



10. Move the arytenoid cartilages backward and forward, 

 meanwhile watching the inside of the larnyx from its lower 

 opening. The projecting ridges, which meet just back of the 

 Adam's apple, are the Vocal Cords. What effect is produced 

 on the vocal cords by the movements of the arytenoid car- 

 tilages ? 



11. Observe the connection of the thyroid cartilage with 

 the cricoid by means of a downward projection of the former. 

 Cut away all of this half of the thyroid cartilage. Notice the 

 slender Hyoid Bone loosely connected with v the upper horn of 

 the thyroid. 



12. Examine now the muscles which move the arytenoid 

 cartilages. 



(a) On each side of the posterior surface of the cricoid is 

 a muscle passing upward to be attached to the corresponding 

 arytenoid ; this is the Posterior Crico-arytenoid Muscle. Dis- 

 sect it loose from the cricoid at its origin below. By pulling, 

 determine its action on the arytenoid, and through the aryte- 

 noid on the vocal cord. 



(b) Arising from the upper edge of the side of the cricoid 



