STRANDED AT LONGNIDDRY. 239 



as a diverticular prolongation of the mucous membrane between the thyroid 

 and cricoid cartilages, accompanied by an imperfect development of the crico- 

 thyroid membrane. 



The air entering the lungs during inspiration would have to pass from the 

 glottis into the trachea through the fissure between the posterior horns of the 

 arytenoids ; but the air, entering the laryngeal pouch, would pass into it below 

 these two horns. The close approximation of these cornua would aid in the 

 closure of the glottis, and in the retention of the air in the lungs when the whale 

 has dived to a depth from the surface. 



The presence of a laryngeal pouch or sac in the B. rostrata, which he dis- 

 sected, had not escaped the acute observation of John Hunter. In his 

 account of that animal he says,* " The arytenoid cartilage on each side sends 

 down a process, which passes on the inside of the cricoid, being attached to a 

 bag which is formed below (behind) the thyroid, and before (below) the cricoid ; 

 these processes cross the cavity of the larynx obliquely, making the passage at 

 the upper part a groove between them." Sandifort t then pointed out and 

 described its arrangements in two foetuses of Balcena mysticetus. Knox ob- 

 served it \ not only in B. rostrata, and B. mysticetus, but in his great northern 

 Rorqual, and he specially directed attention to the mode in which it was 

 supported by the posterior horns of the arytenoid cartilages. Eschricht has 

 also recognised this sac not only in the foetus of B. rostrata, but in that of 

 the Megaptera longimana§ and Reinhardt and he have anew carefully 

 described it in the Greenland Right Whale. A description, with several 

 figures, of the sac in B. rostrata has recently been published by Messrs Carte 

 and Macalister.|| 



Of these authors the last named alone discuss the probable use of this very 

 remarkable pouch. They consider, that by the contraction of its muscular walls, 

 it may expel the contained air so as to augment the power of, and to sustain the 

 expiratory current. They suggest that it might aid in the production or modu- 

 lation of sound, if the whales possessed such a faculty, but think that the size 

 of its aperture, and the absence of all constricting bands, or apparatus, militate 

 against that view of its use. 



The powerful muscular wall of the sac is unquestionably for the purpose of 

 permitting the contraction of the wall on the contents, and as the pouch com- 

 municates above directly with the glottis, a rapid contraction of the investing 

 muscle would aid the expiratory act. But there is another purpose to which 

 this sac may be applied. It may serve the office of a reservoir in which a 



* Structure and Economy of Whales. 



•f* Nieuwe Verhand. van Wetensch. te Amsterdam, 1831. 



\ Catalogue, pp. 11, 17, 23. § Die Nordischen Wallthiere, p. 103, e. s. 



|| Op. cit., p. 236, e. s. 



