38 



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

 formed by a ligameutous or fibrous substance, the boundaries of 

 ■vvhich 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 musele, called hyo-epiglottideus, is, ho\vever, continued from 

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

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

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

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

 eles, -vvhich derive a broad and extensive origin from the posterior 

 and extenial ridges of the arytenoid cartilages, and converge to be 

 inserted into a small round cartilage in the posterior interspace of 

 the arytenoids. These museles, through the advantage alForded to 

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

 garded as their point of origin), act ■n'ith 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 obliąuely backward3 from the intemal 

 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 

 forvvards 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-tube : of these, the first of these is remarkable 

 for its superior size, -vvhich 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 Balcmidce the tracheal 

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

 spirai disposition of the cartilages of the air-tubes, of \vhich Home 

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

 Steller in the Northern Manatee. It is a structure -vvhich best 

 facilitates the lengthening and shortening of the lungs, -vvhose change 

 of bulk in respiration, o\ving to their peculiar form and position, pro- 

 bably takes place chiefly in that direction. 



" Amongst the true Cetacea \ve have observed that it is those -vvhich 

 subsist on the lovvest organized animal substance, as the Baltsnidce, 

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

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

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

 The epiglottis and arytenoid cartilages, for example, are relatively 

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

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

 larynx only at their base ; and not -vvrapped together or surrounded 



