RESPIRATORY ORGANS. 249 
erect with its apex directed craniad to allow the passage of air 
to the lungs, or, as in the act of swallowing, it is turned caudad 
over the aditus laryngis so as to allow food to pass over it and 
into the cesophagus. 
‘The vocal cords are two fibrous elastic bands. Each is 
attached at one end to the apex of the arytenoid cartilage, and 
at the other end to the median ridge on the dorsal surface of 
the thyroid. Each supports a projecting fold of mucous mem- 
brane, the vibration of which causes the voice. 
MUSCLES OF THE LARYNX.—1. Muscles moving the entire 
larynx. 
A. Elevators. M. thyreohyoideus (Fig. 96, p, page 229). 
—A flat band on the lateral side of the larynx. 
Origin on the lateral part of the caudal border of the- 
thyroid cartilage. 
Insertion on the medial two-thirds of the caudal border of 
the caudal cornu of the hyoid. 
Action.—Raises the larynx. 
The stylohyoid (Fig. 65, d, page 109) and the median and 
inferior constrictors (Fig. 96, 7 and £) of the pharynx, already 
described, have the same action. 
B. Depressors.—The sternothyroid (Fig. 65, g’), already 
described (p. 141). 
2. Muscles which move the parts of the larynx one upon 
another. 
A. Muscles on the Outer Surface of the Larynx. 
M. cricothyreoideus (Fig. 96, ).—A broad flat band 
which with its fellow covers the ventral surface of the cricoid 
cartilage and the cricothyroid ligament. 
Origin.—The lateral half of the ventral surface of the cricoid 
cartilage. The muscles diverge so as to leave a part of the 
cricothyroid ligament between them. 
Insertion. —The ventral part of the caudal border of the 
thyroid cartilage laterad of the median ventral notch. 
M. cricoarytenoideus posterior (Fig. 105, 4).—The two 
muscles cover the dorsal surface of the larynx. 
Origin.—From the dorsal part of the caudal border of the 
cricoid cartilage (3) and from its median dorsal crest. The 
