1901,] LARYNX OF CERTAIN WHALES. 283 



The cricoid cartilage differs from the form usual in mammals in 

 that it is incomplete ventrally ; it consists of a great dorsal plate, 

 which curves round the sides and is produced backwards, towards 

 the ventral face, into two " horns " or processes. (Plate XX Vi. 



We may, therefore, distinguish a body and a pair oE cornua. The 

 body is nearly square ; when seen from the dorsal surface, its 

 anterior margin is nearly straight in the middle line, though the 

 corners are obliquely truncated to bear the arytenoid cartilage ; 

 the posterior margin is produced backwards in the middle Ime, to 

 form a somewhat rounded prominence, with which, m this young 

 individual, 4 or 5 of the upper tracheal rings are continuous. 



The dorsal surface is almost flat, shghtly concave m the midd e. 

 As this broad plate of the cricoid curves round the side of the 

 larynx its longitudinal diameter diminishes. 



the anterior margin, beginning at the arytenoid facet, commences 

 to slope gently backwards, and the inclination increases as the 

 ventral surface is reached, till it makes an abrupt backwardly- 

 directed curve near the middle hue, giving rise to a rounded angle ; 

 the margin then continues nearly straight backwards to constitute 

 the ventral or inner edge of the cornu of the cricoid. 



The posterior margin, meanwhile, is mchned forwards from the 

 mid-dorsal line towards the thyroid facet, but the inclination is 

 slight; beyond this point it is continued forwards for a short 

 distance and then curves backwards, forming a shallow lateral bag 

 in the cricoid ; their margin then passes nearly directly backwards 

 to form the dorsal or outer edge of the cornu. _ 



The f^ornu itself is not so deanitely marked off from the cricoid 

 as is the cornu of the thyroid from its body, it is rather the 

 ventral posterior angle drawn out backwards to form on each side 

 a short parallel bar for the support of the peculiar " sublaryngeal 

 pouch " of the Mystacocete. 



As to measurements, the cricoid is 3 inches long in the micl- 

 dorsal line and 3 inches across, taken from the lower edges of the 

 arytenoid facets, and the same between the thyroid fac-ets, while 

 the space between the two arytenoid facets is 1^ inches, ihe 

 lateral margin, as seen from the back, i. e. the distance from the 

 outer edge of the arytenoid facet to beyond the thyroid facet, is 



O ITlCilBS 



The ventral margin of the cricoid (or rather of its cornu) is 

 2 inches ; the dorsal or outer edge of the cornu is 1| inches. 



In the text-books, both of Owen and Huxley, the ventral 

 incompleteness of the cricoid is mentioned. _ 



Carte and Macahster give no clear figure of the cricoid, and 

 do not represent the ventro-posterior cornua ; but m the text 

 this " tongue- shaped process " is described as reaching to the first 

 ring of the trachea. In the present youthful specimen it extends 

 backwards to the sixth ring. • , cc u i " 



The arytenoid cartilage consists of a somewhat conical body 

 or processus muscularis, of a stout cylindro-conical posterior 



