530 RESPIBATORT APPABATUS IN MAMMALIA. 



articulates with the middle part of the thyroid ; it gives origin, posteriorly, to 

 two lateral prolongations, which pass to the inferior border of the aiytasnoids, 

 but usually without joining these. 



The summit unites the free portion of both borders, and is thi'own forwards 

 on the upper face of the soft palate. 



Arytaenoid Cartilages (Fig. 311, a, a'). These two pieces have been so 

 designated from their resemblance, when approximated, to the mouth of a pitcher 

 (apvratva, £?8os, " like a pitcher "). They are situated in front of the cricoid, 

 above the entrance to the larynx ; each has an irregular quadrilateral form, and 

 presents for study tivo faces and four borders. The internal face is smooth, 

 almost flat, and lined by the laryngeal mucous membrane. The external face is 

 divided by a ridge into two portions : a superior, covered by the aryttenoid muscle ; 

 and an inferior, giving attachment to the thyro-arytasnoid and lateral crico- 

 arytsenoid muscles. The snpen-ior border is concave, and joined to that of the 

 opposite cartilage (by means of the ligamentum crico-ctrijtcenoideum). The inferior 

 border {processus voccdis) gives attachment, posteriorly, to the vocal cord. The 

 anterior border, thick and convex, and covered by the mucous membrane, circum- 

 scribes, superiorly and laterally, the entrance to the larynx ; it is in joining 

 above, with the homologous border of the other arytaenoid cartilage, that the 

 pitcher-beak already mentioned is formed. The posterior border projects into the 

 larynx by its inferior portion ; superiorly, this border is very thick, and is 

 hollowed by a small articular facet, which articulates with the anterior facet of 

 the bezel of the cricoid. Above, and to the outside of this facet, is a very promi- 

 nent tubercle {processus muscularis) that terminates behind the crest of the 

 external face, and gives attachment to the posterior crico-arytsenoid muscle. 



Aeticulations of the Laryngeal Caetilages (Figs. 312, 313).— These 

 are of the simplest kind. They are as follows : — 



A. The thyroid cartilage is joined to the os hyoides : 1. At the extremities 

 of the cornua, by means of a short ligament interposed between that extremity 

 and the appendix of the superior border of the thyroid. 2. To the whole extent 

 of the hyoid concavity, by an elastic membrane — the thyro-hyoid membrane, 

 attached to the body of the thyroid cartilage and the superior border of the lateral 

 plates of that cartilage (Fig. 313, 4). 



B. The thyroid cartilage articulates with the cricoid by two small arthrodiae, 

 which unite the posterior extremities of the branches of the first cartilage to the 

 facets on the external face of the second. A thin external capsule encloses this 

 articulation (Fig. 312, 2). These two cartilages are also held together by means 

 of a membranous elastic ligament — the crico-thyroid membrane, which passes from 

 the angle comprised between the two branches of the thyroid to the anterior notch 

 of the cricoid (Fig. 313, 3). 



C. The two arytaenoid cartilages are united, at their superior border, by the 

 arytenoid muscle and laryngeal mucous membrane. 



D. The latter cartilages come in contact with the anterior facets of the cricoid 

 bezel, by means of the concave articular surface of their posterior border ; the 

 result is a small, but veiy movable, arthrodial joint, enclosed by a thin external 

 capsule and by the surrounding muscles (Fig. 312, 1). 



E. These cartilages are also united to the thyi'oid, through the medium of 

 the vocal cords. These are two elastic bands which project within the larynx, 

 and between them include the triangular space termed the glottis ; their internal 

 face is covered by the mucous membrane of the larynx ; the thyro-hyoid muscles 



