THE LABYNX. 149 



away this muscle from one side and see that the cri- 

 coid 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 aryte- 

 noid cartilages. 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. With one hand move the arytenoid cartilages back- 

 ward and forward, meanwhile watching the inside of 

 the larynx 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 carti- 

 lages ? 



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 the upper bone of the thyroid. 



12. Examine now the muscles which move the arytenoid 

 cartilages. 



a. On each side of the posterior surface of the cri- 

 coid is a muscle passing upward to be attached to 

 the corresponding arytenoid; this is the poste- 

 rior crico-arytenoid muscle. Dissect it loose 

 from the cricoid, at its origin below. By pulling, 

 determine its action on the arytenoid, and through 

 the arytenoid on the vocal cord. 



b. Arising from the upper edge of the side of the 

 cricoid cartilage, and passing upward and back- 

 ward to the arytenoid, is the lateral crico-aryte- 



