304 Zoological Society. 



that I have only to observe the close agreement with these accounts 

 which the structure of the parts presented in the three Dugongs dis- 

 sected by me ; Daubenton* and Humboldtf describe and figure a 

 precisely similar condition of the respiratory apparatus in the Ma- 

 natee. Steller describes the same extension of the lungs along the 

 dorsal aspect in the Stellerus, which he aptly compares to the posi- 

 tion of the lungs in the bird, but without their fixation to the pari- 

 etes of the chest, so characteristic of that class. The Chelonian 

 reptiles, perhaps, offer a closer resemblance % to the herbivorous Ce- 

 tacea in this respect ; and it is worthy of remark that the air-cells 

 of the lungs are larger in the Dugong than in any other Mammals. 

 In the carnivorous Cetacea the air-cells are remarkably minute, and 

 the lungs more compactly shaped and lodged in a shorter thorax. 



" There are but three true tracheal rings anterior to the bifurcation 

 of the air-tube : the first of these is remarkable for its superior 

 size, which forms an intermediate transition between the cricoid and 

 the second tracheal ring. The tube is somewhat flattened from be- 

 fore backwards ; its circumference is 5 inches ; its antero-posterior 

 diameter 1 inch. In the BalcEnidce 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, probably 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 Balcenidae, 

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

 additional complexity of the ccecum coeli ; 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 together by the membranes of the 

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

 by that membrane as far as their apices, as in the Dolphins. In the 

 Balcenoptera also, the apices of these cartilages are not expanded, as 



* BuiFon, vol. xiii. 



f Wiegmann's Archivfiir Naturgeschic/de, 1838, pi. ii. fig. 5. 



X This resemblance is further exemplified in the shortness of the trachea, 

 the completeness of its cartilaginous rings, the length of the bronchial tubes, 

 and the extension of their cartilaginous structure far into the substance of 

 the lungs in the Dugong. 



