456 CETACEA. 



where they bend backwards is augmented to 0*72 inch. The cricoid cartilage is strong 

 and compact, with a prominent dorsal ridge, which terminates anteriorly in a 

 rounded projection, directed forwards and slightly upwards. The surfaces of the 

 cartilage external to the ridge are concave, and, on looking at them from below, they 

 are seen to have their margin somewhat everted. The margin anterior to the 

 attachment of the arytenoid cartilages is concave, and the articulation for those 

 structures to the cricoid, unlike that of the thyroid, is a capsular synovial joint, which 

 Turner has also observed to be the case in the great Finner {Sihbaldius). The 

 cricoid ring is thick, but there is a great hiatus between it and the posterior border 

 of the body of the thyroid, due to the circumstance that the cricoid cartilage simply 

 roofs in this portion of the cavity of the larynx. The passage through the cricoid 

 ring is an inch broad, by 0*75 inch high. The body of the cartilage becomes much 

 ossified in the adult. 



Each arytenoid is a slightly oval laterally compressed cartilage, more pointed 

 posteriorly than anteriorly, about 1 inch long by 0*70 inch in breadth. It presents 

 three principal surfaces, an anterior, an external, and a posterior. The first is slightly 

 concave in its centre, and its inner margin expands in its upper half into a triangular 

 secondary surface, to which a downward process of the anterior horn is attached. 

 At the upper end of this secondary surface is the narrow isthmus from which the 

 anterior horn is projected. The limited nature of the structural union existing 

 between the body of the arytenoid and its horn, permits the latter to have consider- 

 able mobility. The posterior surface of the body presents the elongated oval 

 depression for articulation with the cricoid. The internal surface is broad above, 

 pointed below and convex, and its posterior margin is continuous above with 

 the upper border of the cricoid articular surface, anterior to which on the apex of 

 the cartilage, and immediately behind the base of its anterior horn, is a small 

 flattened secondary triangular area. The anterior horns are directed upwards and 

 then forwards, so that their anterior borders are concave to rest against the epiglot- 

 tidean cartilage. They are small laterally compressed structures, their inner surfaces 

 being perfectly flat, so that the two cartilages can be closely opposed to each other. 

 Their front and posterior margins are sharp, except in the basal half of the latter, which 

 expands into a flat surface. At the point where the horn springs from the body, and 

 depending from it, a short process rests against the inner margin of the first secondary 

 surface of the body. This process or horn is prolonged backwards, as it were, by a 

 variable number of small cartilages, usually three, closely applied to the inner 

 margin of the anterior surface of the arytenoid, and are thus included in the 

 aryteno-epiglottidean membrane. Anterior to the downwardly projecting process 

 from the base of the anterior horn of the arytenoid, is another narrow rod, arching 

 outwards and downwards, and occasionally divided at its extremity into two. In its 

 position and relation this is the equivalent of the posterior horn of the arytenoid. 

 It is sometimes, however, only connected to the arytenoid by fibrous tissue. Lying 

 between it and the cuneiform cartilages already described, occur two or three other 

 similar yellow cartilages, but varying in number and size. The largest is about 0*25 



