MUSCLES OF THE LARYNX 519 
of the thyroid cartilage. Its action is to draw the larynx toward the root of the 
tongue. It is related laterally to the external maxillary vein and the anterior part 
of the mandibular gland. 
The hyo-epiglotticus (M. hyo-epiglotticus) is a feeble muscle which occupies a 
median position above the central part of the thyro-hyoid membrane, enclosed by 
an elastic sheath, the hyo-epiglottic ligament. It arises from the body of the hyoid 
bone by two branches which unite and are inserted into the front of the base of the 
epiglottis. Its action is to draw the epiglottis toward the root of the tongue. 
B. Intrinsic Muscies 
The crico-thyroideus (M. crico-thyreoideus) is a short muscle which fills the 
groove on the lateral surface of the cricoid cartilage; its fibers are directed dorsally 
and somewhat forward. It arises from the ventral part of the lateral surface and 
posterior edge of the cricoid cartilage, and is inserted into the posterior border and 
Fie. 462.—LarynceaLt Muscies or Horse, SEEN FROM Lerr Sipe ArreR REMOVAL OF Masor Part or LAMINA OF 
TuHyrorw CaRTILAGE. 
a, Kerato-hyoideus; 6, thyro-hyoideus; c, crico-thyroideus; d, sterno-thyroideus; e, ventricularis; /, vocalis; g, 
crico-arytenoideus lateralis; A, crico-arytenoideus dorsalis; i, arytenoideus transversus; 1, lingual process; 2, small 
cornu, 3, thyroid cornu, of hyoid bone; 4, thyroid cartilage; 5, cricoid cartilage; 6, epiglottis; 7, apex of arytenoid 
cartilage; 8, trachea; 9, muscular process of arytenoid; 10, lateral lobe of thyroid gland; 10’, isthmus of thyroid gland; 
11, laryngeal saccule. The saccule is larger than it is represented in this figure, and extends almost to the vocal 
process. (Ellenberger-Baum, Anat. d. Haustiere.) 
adjacent part of the lateral surface of the lamina of the thyroid cartilage. Its 
action is to draw the thyroid cartilage and the ventral part of the cricoid cartilage 
together. In this action the cricoid cartilage is probably rotated about a trans- 
verse axis through the crico-thyroid joints, carrying the bases of the arytenoid 
cartilages with it and thus tensing the vocal cords. 
The crico-arytenoideus dorsalis (M. crico-arytzenoideus dorsalis)! is a strong, 
somewhat fan-shaped muscle, which, with its fellow, covers the dorsal surface of 
the lamina of the cricoid cartilage. It is partially divisible into two layers. It 
has a broad origin on half of the lamina of the cricoid cartilage, including the me- 
dian ridge, and its fibers converge to be inserted into the processus muscularis of 
the arytenoid cartilage. Its action is to dilate the rima glottidis by rotating the 
arytenoid cartilage so as to carry the vocal process and cord outward (abduction). 
The crico-arytenoideus lateralis (M. crico-arytenoideus lateralis) lies on the 
medial face of the thyroid lamina. It arises from the anterior border of the lateral 
part of the arch of the cricoid cartilage. The fibers pass in a dorsal direction and 
converge on the processus muscularis of the arytenoid cartilage. It closes the 
rima glottidis by rotating the arytenoid cartilage inward (adduction). 
——— ee 
1 Also known as the crico-arytenoideus posterior s. posticus. 
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