CARTILAGES OF THE LARYNX 



441 



between the parotid p;lan(ls.' Its long axis is practically horizontal when the head 

 antl neck are extended (Fig. 254). 



It is related dorsally to the pharynx and the origin of the oesophagus. Ven- 

 trally it is covered by the skin, fascia, and sterno-hyoid and omo-hyoid muscles. 

 Laterally it is related to the parotid and submaxillary glands and to the internal 

 pterygoid, stylo-maxillaris, digastrieus, stylo-hyoid, and pharyngeal const I'ictor 

 muscles. 



It is attached to the body and thyroid cornua of the hyoid bone, and thus in- 

 directly to the base of the cranium. 



Its cavity communicates anteriorly with the ]:)harynx and (potentially) with 

 the mouth; posteriorly, with the trachea. 



The wall of the larynx consists of a framework of cartilages, connected by 

 joints and ligaments or membranes, and moved by extrinsic and intrinsic muscles. 

 The cavity is lined with mucous membrane. 



Cartilages of the Larynx 

 There are three single cartilages and one pair; the single cartilages are the 

 cricoid, thyroid, and epiglottis; the arytenoid cartilages are paired. 



Fig. 349. — LARYNfiF.Ai, Cartilages of Horse, Right View. 



The cricoid cartilage (Cartilago cricoidea)'is shaped like a signet ring. The 

 dorsal part is a broad, thick, quadrilateral plate termed the lamina ; the outer 

 (dorsal) surface of this is marked by a median ridge separating two shallow cavities, 

 which give attachment to the posterior crico-arytenoid muscles. On either side 

 of these depressions are two articular facets. The anterior facets (Facies articu- 

 lares arytsenoidese) are placed at the anterior border, are oval and convex, and 

 articulate with the arytenoid cartilages. The posterior facets (Facies articulares 

 thyreoideffi) are situated on the front of a ridge, a short distance from the posterior 

 border; they are concave, and articulate with the posterior cornua of the thyroid 

 cartilage. The ventral and lateral parts of the ring are formed by a curved 

 band, called the arch (Arcus), which is narrowest below. The lateral surfaces 

 of the arch are grooved for the crico-thyroid muscle. The anterior border of the 



1 In the ordinarj' position of the head and neck, and while the parts are at rest, about half 

 of the larynx lies between the })ranches of the mandible; when the head and neck are extended, 

 proportionately more of the larynx lies behind a plane through the posterior borders of the rami. 

 It is here described in the position it occupies when the head and neck are extended. 



