612 



Comparative Morphology of Chordates 



consists of a fold of the skinlike investing layer of the "hard" palate. 

 It prolongs the nasal passages backward, but as a single or undivided 

 passage, separating the original pharynx into an upper nasopharynx 

 and a lower buccal division (Fig. 469). 



Trachea 



The anterior region of the trachea is enlarged to form the larynx, 

 containing the vocal apparatus (Figs. 470, 471). The walls of the 

 larynx are supported by cartilages. The most anterior and largest of 

 them is the thyroid, which encloses the larynx ventrally and laterally 

 but not dorsally. Attached to its mid ventral anterior edge and freely 

 projecting forward is a flap of tissue consisting internally of elastic 

 fibrocartilage and covered externally by a continuation of the mucous 

 membrane which invests all neighboring surfaces. This flap, the epi- 

 glottis, is usually rounded or oval in outline, its form being such that, 



Fig. 470. {Left) Front view of the human laryngeal cartilages and ligaments. 

 (Sappey.) (1) Hyoid bone; (2) its large cornua; (3) its small cornua; (4) thyroid 

 cartilage; (5) thyrohyoid membrane; (6) lateral thyrohyoid ligament, containing 

 the cartilago triticea (7); (8) cricoid cartilage; (9) cricothyroid membrane; (10) 

 lateral ceratocricoid ligaments; (11) uppermost ring of trachea. 



{Center) Back view of the laryngeal cartilages and ligaments. (Sappey.) (1) 

 Thyroid cartilage; (2) cricoid cartilage; (3) arytenoid cartilages; (4) their muscular 

 processes; (5) ligament connecting lower cornu of thyroid with back of cricoid 

 cartilage; (6) upper ring of trachea; (7) epiglottis; (8) ligament connecting it to 

 the angle of the thyroid cartilage. 



{Right) Muscles of the larynx, as seen from the right side. (Sappey.) (1) Hyoid 

 bone; (2, 3) its cornua; (4) right lamina of thyroid cartilage; (5) posterior part of 

 same, separated by oblique line from anterior part; (6, 7) superior and inferior 

 tubercles, at ends of oblique line; (8) upper cornu of thyroid; (9) thyrohyoid 

 ligament; (10) cartilago triticea; (11) lower cornu of thyroid, articulating with 

 cricoid; (12) anterior part of cricoid ; (13) cricothyroid membrane; (14) cricothyroid 

 muscle; (15) posterior cricoarytenoid muscle, partly hidden by thyroid cartilage. 

 (Courtesy, Symington: "Quain's Anatomy," London, Longmans, Green & Co., 

 Ltd.) 



