THE LARYNX. 421 
THE THYROID CARTILAGE (Oupeds, a shield, eidos, like) is composed of two 
lateral plates, each presenting the form of an oblique-angled parallelogram, 
joined together in front, and separated by a considerable space behind, 
which is occupied by the cricoid cartilage. The point in front, which 
corresponds with the pomum Adami in man, is called the body. The 
posterior angles of the lateral plates are each terminated by a prolonga- 
tion, called a cornea or ala—the two superior being united by ligaments 
to the os hyoides, and the two inferior to the cricoid cartilage. In the 
upper part of the anterior angle is fixed the epiglottis, by means of the 
union called amphiarthrosis. 
THE CRICOID CARTILAGE (kpikos, a ring, eidos, like) is a complete ring, 
but it is much deeper behind than 
before. It is somewhat depressed 
from side to side, especially in those 
horses which are deficient in wind. 
On the upper edge behind it has two 
rounded surfaces, which articulate 
with the arytenoid cartilages. In 
the middle is a vertical ridge, to 
which the csophagus is united by 
cellular membrane, and on each side 
of this is a hollow for the lodgment 
of muscles. 
THE ARYTENOID CARTILAGES (dpv- 
taiva, a pitcher, eidos, like), two in 
number, are triangular in form, 
broad and thick below, and pointed 
above. They give attachment to 
the vocal chords, and are the means 
by which these are rendered tense 
or lax, open or close, by the action 
of the muscles of the larynx. 
THE EPIGLOTTIS (émvyAGrts) is a 
cartilage of a heart shape, attached 
to the angle between the lateral + Fic. 7.—Posrerior View or rue Os Hyorpes 
plates of the thyroid cartilage. ae 
When pressed backwards, it closes 
the rima glottidis or fissure between 
the vocal chords, and in this way 
prevents the food from passing into 7. 7. Long horns of the os hyoides. 
the larynx. our completing the back of the 
By THE AID OF THESE CARTILAGES, 9. 9. 9. ‘Tracheal rings incomplete behind 
and of. the ligaments connecting 10. 10 posaombne between the rings of the 
them, as well as by means of the 
muscles which move them, a triangular opening called the rima glottidis 
is formed, having its base behind at the arytenoid cartilages and its 
apex in front, below the epiglottis. The sides of this opening are formed 
by ligamentous bands, attached to the arytenoid cartilages, so that as 
these are drawn backwards they are rendered tense; and if they are 
drawn apart the rima or fissure is widened and admits more air. When 
this fissure is contracted, either by thickening of the edges or by the 
wasting of the muscles which keep it open, roaring or whistling is 
produced ; so that it is important to arrive at a correct idea of its 
mechanism. 
. Epiglottis. 
. Arytenoid cartilages. 
. Cricoid cartilage. 
. Spur process, or appendix of the os hyoides. 
. 5. Branches of the body of the os hyoides. 
. 6. Short horns. 
COMA os wre 
