384 CETACEA. 



Eustachian tithe and gnttural sacs.' — The eustachian tube opens into the sac 

 of the posterior nares on a line with the posterior margin of the soft palate, a very 

 short way above the inner border of the thick constriction of the nasal orifice. I had 

 an opportunity of examining these parts only in the foetus, in which the eustachian 

 orifice is 0-2 inch above the part indicated. It is an oval slit from before forwards 

 0'02 inch in length, and it is situated in the centre of one of the thickened bands 

 which surround the arched crypts. It leads into a short passage which runs up the 

 wall of the sac for a little distance ; then it bends upon itself, running oLitwards 

 and slightly backwards as a passage 0-10 inch broad, which gives off small lateral 

 passages protected by valvular folds, and which burrow in the textures surrounding 

 the mucous wall of the posterior nares, in the same way as the similar passages in 

 Flatanisla, but not to the same extent. It thus crosses the pharynx, but I have 

 not had the opportunity to trace it to the internal ear. As it reaches the outer wall 

 of the pharynx it gives off three sacs much smaller than in Platanistu, and which 

 lie between the stylohyal and the anterior corner of the tliyroid cartilage. These 

 sacs lie one aboA'e the other, and the most superior is closely related to the thyroid 

 cartilage ; all are directed downwards and backwards ; the most inferior burrowing 

 downwards in the direction of the body of the thyroid cartilage. Each sac has the 

 same structure as in Platanista, but I cannot detect any tendinous bands connected 

 intli folds like those that occur in that genus. It must be borne in mind also that 

 the sacs are mere rudiments in this foetus compared with those of Flatanista. 



It will be observed that the cartilages of the larynx of the species are sur- 

 rounded with little cavities, possessing much the same characters as the finer 

 passages of the guttm'al sacs. It has occurred to me that if materials existed to 

 trace out the ramifications of these structures, they would j^robably be found to have 

 some communication with the curious sinuous passages which surround the larynx. 

 If any connection should be proved to exist between them, it would seem as if 

 these finer ramifications of the guttm-al sacs being filled with air must exercise 

 some influence in depurating the blood in the vessels surrounding the larynx, and 

 thus contribute to the functional activity of the complex mechanism of the orifice 

 of the respiratory tube. 



Larynx (Plate XXVIII, fig. 2). — The tube of the larynx of Orcella presents 

 certain differences in its foetal and adult condition. It may be premised, however, 

 that it has the general characters distinctive of the Cetacea, but differs from that 

 of Flatanista in its much greater length, although its opening is shorter, and in 

 the narrow character of its aryteno-epiglottidean folds. In an adult, of about the 

 same size as the Flatanista from which the laryngeal measurements of that species 

 were taken, the opening was only 0-80 inch long. In the foetus the tube was 

 projected 0-82 inch up the posterior nares. The epiglottis projected beyond the 



■ For remarks on the guttural pouch of Cetacea, see particularly Hunter's Memoir in Phil. Trans, and his essays 

 and observations; also Eschricht on the Gangetic Dolphin, Danish Transactions, 5th ser. vol. ii. 1851, and translated ; 

 Annals and Mag. Nat. Hist. 1852, vol. ix. p. 174; and Murie, op. cit. ; Huxley's Anat. of Vert«b. An. 1871, 

 pp. 410, &c. 



