132 PHYSIOLOGY FOR THE LABORATORY. 



of the cartilaginous rings of the trachea and 

 might easily be mistaken for one. Move it 

 up and down to see that it is separate from 

 the thyroid and the trachea. Trace it around 

 to the dorsal side underneath the lower pos- 

 terior corner of the thyroid cartilage. How 

 far on the dorsal side does it extend ? What 

 is its exact shape? How is it articulated 

 with the thyroid cartilage? 



3. On the dorsal side above the cricoid cartilage on 

 either side is an arytenoid cartilage. It is con- 

 cealed by the muscles and the vocal cord, 

 but its exact shape can be found after dis- 

 secting the muscles. 



g. The muscles. 



1. A crico-thyroid muscle is on either side of the 



dorsal surface extending from the thyroid to 

 the corresponding cricoid cartilage. 



(1) Where is it attached on each cartilage ? 



(2) What is its use ? 



(3) Dissect it away and find how the motion 



of the thyroid is limited. 



2. The posterior crico-arytenoid muscles are on the pos- 



terior surface of the cricoid, one at either 

 side. They extend diagonally upward to 

 the corresponding arytenoid cartilages. Dis- 

 sect away the attachment on the thyroid 

 cartilage, pull the muscle, and note the effect 

 on the arytenoid cartilage and on the vocal 

 cord. 



