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 (1), cricoid (3), and 
epiglottic (2), and two paired cartilages, the arytenoids (4). 
The thyroid cartilage (cartilago thyreoidea) (1) 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- 
Fic. 104.—CARTILAGES OF LARYNX, WITH SIDE VIEW oF Hyorp Bone, 
&, ceratohyal; c, epihyal; d, stylohyal; ¢, tympanohyal; /, thyrohyal, 1, 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 (f). 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 
