VOICE AND SPEECH. 



567 



and give a rhomboid form to the glottis. Thus it is materially 

 widened. 



3. The Lateral Crico-arytenoids. These muscles are found upon 

 the inner side of the cricoid. They are carried backward and upward 

 and are fastened to the outside of the posterior ends of the bases of 

 the arytenoid cartilages. 



Action. In contracting they rotate the arytenoid cartilage in- 

 ward. They are antagonists of the posterior crico-arytenoid muscles; 

 they narrow the vocal part of the glottis. 



4. The Thyro-arytenoid Muscles. This pair of muscles is inserted 

 at the anterior end in the middle of the angle of the thyroid cartilage, 



Fig. 211. Schematic Closure of the Glottis by the Thyro-arytenoid 

 Muscles. ( LANDOIS . ) 



//, //, Position of the arytenoid cartilages during quiet respiration. The 

 arrows indicate the direction of muscular traction. I, I, Position of the 

 arytenoid cartilages after the muscles contract. 



1 at the posterior end it is fastened to the inside of the anterior end 

 the base of the arytenoid cartilages. Each muscle of the pair 

 ; its entire length parallel with the corresponding vocal cord. 

 This muscle has two bundles : an internal and external bundle, 

 muscle draws the arytenoids toward the thyroid and relaxes the 

 By the internal bundle the anterior part of the vocal cord 

 be tightened while relaxing the posterior part. It is the muscle 

 teemed in the production of the high notes in the singing voice. 



, The arytenoid constitutes an odd muscle. It extends pos- 

 teriorly between the two arytenoid cartilages. The muscle is divided 

 into two layers: one posterior, of oblique fibers disposed like an X; 

 one anterior, of transverse fibers. 



