566 PHYSIOLOGY. 



THE MUSCLES. All of the laryngeal cartilages, joined together 

 by ligaments, are moved by five pairs of muscles. The muscles of the 

 larynx are divided into two groups: intrinsic and extrinsic. To the 

 former group belong those muscles which are attached to the various 

 cartilages. The latter collection comprises the musculature connect- 

 ing the larynx to other parts like the hyoid bone. 



INTRINSICS. Of these there are five pairs. 



1. The Crico-thyroid Muscles. These, which are in the anterior 

 part of the larynx, originate in the front and sides of the cricoid car- 

 tilage below. Outwardly they are attached on each side to the lower 



Fig. 210. Schematic Horizontal Section of Larynx. (LANDOis.) 



/, Position of horizontally divided arytenoid cartilages during respiration. 

 From their anterior processes run the converging vocal cords. The arrows 

 show the line of traction of the posterior crico-arytenoid muscles. //, //, 

 Position of the arytenoid muscles as a result of this action. 



edge of the thyroid cartilage. They become fixed by the action of 

 the thyro-hyoid, sterno-thyroid, and laryngo-pharyngeal muscles. 



Action. They incline the cricoid cartilage upward and backward 

 and so elongate and stretch the vocal cords, at the "same time contract- 

 ing the opening of the glottis. 



2. The Posterior Crico-arytenoid Muscles. These take their de- 

 parture from the posterior surface of the shield of the cricoid cartilage. 

 They then converge and are fastened to the base of the corresponding 

 arytenoid cartilage. 



Action. In contracting they turn the anterior ends of the aryte- 

 noids outward, whereby they separate the vocal cords from each other 



