RESPIRATORY ORGANS. 247 



and widened by the action of muscles. The vocal cords, which 

 bound it, are set vibrating by currents of air transmitted from the 

 lungs, and the voice-sounds are thus produced. The caudal 

 portion (inferior portion) of the laryngeal cavity is that between 

 the glottis and the first tracheal cartilage. It is narrowed near 

 the glottis. 



CARTILAGES OF THE LARYNX (Fig. 104). There are 

 three unpaired cartilages, the thyroid (i), cricoid (s), and 

 epiglottic (2), and two paired cartilages, the arytenoids (4). 



The thyroid cartilage (cartilage thyreoidea) ( i ) has nearly 

 the form of a visor of a cap, but is relatively broader at its ends 

 than a cap visor. It forms about two-thirds the circumference 

 of a circle, and is so situated that it embraces the other carti- 



FIG. 104. CARTILAGES OF LARYNX. WITH SIDE VIEW OF HYOID BONE. 

 l>, ceratohyal; c, epihyal; d, stylohyal; e, tympanohyal; f, thyrohyal. I, thyroid 

 cartilage; 2, epiglottis; 3, cricoid cartilage; 4, arytenoid cartilage; 5? cricothyroid 

 ligament; 6, thyrohyoid ligament; 7, trachea. 



lages ventrally and laterally. Its caudal and cranial borders 

 are oblique to its caudocranial axis and are directed dorso- 

 caudad. To the middle of the cranial border is attached the 

 epiglottic cartilage (2), and the whole cranial margin is con- 

 nected by membrane ( 6 ) to the body and caudal cornua (/") 

 of the hyoid bone. The dorsal border projects craniad into a 

 considerable cornu which is attached to the free end of the 

 caudal hyoid cornu (/"). The border also projects caudad into 

 a process which articulates with a facet on the lateral surface 

 of the cricoid cartilage (3). In the middle of the dorsal surface 



