ON THE GREENLAND RIGHT-WHALE. 101 



i. Lie/amentum thyreo-cricoideum inferius. 



k. The epiglottis. 



/. Ligamentum thyreo-epiglottideum. 



m. The chief piece or body of the arytenoid cartilage. 



11. The anterior or ascending cornu of the same. 



0. The posterior or descending cornu of the same. 



p. The transverse ligament between the posterior cornu of the arytenoid carti- 

 lages. 



r. The exterior or dorsal surface of the cricoid cartilage. 



s. The interior or ventral surface of the same. 



t. A ligamentous membrane betvreen the lateral edges of the cricoid cartilage and 

 the posterior cornua of the arytenoid cartilages. ;, 



u. The anterior part of the sacculus of the trachea, as seen from the side in its 

 place between the posterior cornua of the thyroid and arytenoid 

 cartilages. 



We know that the most essential peculiarity of the larynx of the whalebone-whales, as 

 compared with that of the toothed-whales, consists in its allowing the mucous membrane of the 

 respiratory canals, by means of an opening on its ventral surface, to appear in the form of a sac 

 with an exterior covering of a strong layer of muscles. A similar sac is found on the 

 respiratory canals of many terrestrial mammals, as is very well known ; in most cases it appears 

 between the hyoid bone and the thyroid cartilage, though in others, especially in some of the 

 apes, between the thyroid and cricoid cartilages, or between the latter and the first ring of the 

 trachea, and the last-mentioned case most resembles that of the whalebone-whales, although 

 these latter have also some characteristics pecuUar to themselves, which have already been 

 distinctly pointed out in earlier researches. Of the cricoid cartilages only the posterior half 

 (fig. 1, r) is present, which accordingly has too free lateral margins (figs. 2 and 6, r), whereas the 

 arytenoid cartilages are continued towards the ventral surface in a pair of processes (figs. 2 and 

 5, o), which run for a considerable extent along these lateral edges of the cricoid, though always 

 with a certain interval, closed by means of a ligamentous membrane (fig. 5, t), but which at 

 length approach each other in the mesial line of the ventral surface, where they are united by 

 means of a special ligament (fig. 2, q). The arytenoid {m) have accordingly, besides their two 

 usual prolongations, or cornua (n), which on the dorsal side strengthen the opening of the 

 respiratory canals into the nasal cavity, still two other cornua running in the opposite direction, 

 which together form a complete frame round that opening which connects the respiratory canals 

 with the air-sac on the ventral surface of the larynx. The opening, however, does not extend 

 quite to the hindmost connecting ligaments of the two cartilaginous prolongations, being here 

 somewhat diminished by a fold of the mucous membrane. 



In the rorquals the plate of the thyroid is short, the posterior or descending cornua of 

 the arytenoid cartilages just mentioned are almost entirely uncovered by it, and the opening of 

 the air-sac may therefore be said to be placed, to a certain degree, on the ventral surface of the 

 larynx, between the thyroid cartilage and that hgament, which in this surface assumes the place 

 of cricoid cartilage. But in the Greenland whale the thyroid plate (fig. 4, e), extends so far back- 

 wards as to cover this opening completely, and in this place it becomes perfectly clear that the 



