Dugong ; the small pyramidal prominence in front of the glottis is 

 formed by a ligamentous or fibrous substance, the boundaries of 

 which cannot be defined, as it passed insensibly into the cellular sub- 

 stance filling the posterior interspace of the divisions of the thyroid, 

 of which cellular substance it seems to be a mere condensation. The 

 usual muscle, called hyo-epiglottideus, is, however, continued from 

 the anterior part of this pseudo-epiglottis. The distance from the in- 

 sertion of the chorda vocales to the apex of the epiglottis is 9 lines. 

 The muscles of the larynx are powerfully developed. The aryteno- 

 idei obliqui and transversi are represented by a single pair of mus- 

 cles, which derive a broad and extensive origin from the posterior 

 and external ridges of the arytenoid cartUages, and converge to be 

 inserted into a small round cartilage in the posterior interspace of 

 the arytenoids. These muscles, through the advantage afforded to 

 them by this middle fixed fulcrum (which ought therefore to be re- 

 garded as their point of origin), act with great power upon the ary- 

 tenoid cartilages, drawing them together, and thus forcibly closing 

 the narrow glottis. They are directly opposed by strongly developed 

 thyreo-arytenoidei, which pass obliquely backwards from the internal 

 and interior part of each division of the thyroid cartilages to the pos- 

 terior and outer part of the arytenoids, which they draw apart, and 

 thus open the glottis. The crico-arytenoidei arise from the anterior 

 border of the cricoid, and are so inserted as to draw the arytenoidei 

 forwards as well as outwards. The crico-thyroidei cover the whole 

 of the fore part of the cricoid cartilage. The sterno-thyroidei, and 

 thyreo-hyoidei are extremely powerful. 



" The thyroid gland formed an irregular bilobed mass, the greater 

 part of which lies in front of the conjoined bronchial divisions of the 

 trachea. There are but three true tracheal rings anterior to the bi- 

 furcation of the air-tul)e : of these, the first of these is remarkable 

 for its superior size, wliich forms an intermediate transition between 

 the cricoid and the second tracheal ring. The tube is somewhat 

 flattened from before backwards ; its circumference is 5 inches ; its 

 antero-posterior diameter 1 inch. In the Balasnidce the tracheal 

 rings are deficient at the anterior part of their circumference. The 

 spiral disposition of the cartilages of the air-tubes, of which Home 

 has given a figure, in the Dugong, is described with more detail by 

 Steller in the Northern Manatee. It is a structure which best 

 facilitates the lengthening and shortening of the lungs, whose change 

 of bulk in respiration, owing to their peculiar form and position, pro- 

 bably takes place chiefly in that direction. 



" Amongst the true Cetacea we have observed that it is those which 

 subsist on the lowest organized animal substance, as the Balcenida, 

 which approach the nearest to the herbivorous species, in having the 

 additional complexity of the ceecum cceli ; and it is interesting to find 

 that the same affinity is manifested in the structure of the larynx. 

 The epiglottis and arytenoid cartilages, for example, are relatively 

 shorter in the Balcenoptera than in Delphinus ; and, as Mr. Hunter 

 has observed, they are connected tpgether by the membranes of the 

 larynx only at their base ; and not wrapped together or surrounded 



