420 DR MORRISON WATSON AND MR ALFRED H. YOUNG 
larynx. Lastly, the arrangement of the muscular fibres which lie in relation to 
the laryngeal pouch is essentially similar in the toothed and in the whalebone 
whales. Dr Muniez,* in his article on Risso’s Grampus, arrives at the conclu- 
sion that these fibres belong to the thyro-arytenoid muscles, and the description 
given above of these muscles in Beluga leaves no doubt of the accuracy of 
this opinion. The same author * observes that the thyro-arytenoid muscles 
in Grampus “evidently correspond to those transversely-striped whorled 
muscular fascicles which surround or form the exterior coat of the so-called 
air bag or laryngeal sac both in the Right, the Pike whale, and the Razor-back.” 
A reference to Professor TuRNER’st description of these fibres in Balenoptera 
Sibbaldii and to that of CarTE and MacatisTer{ of the same in Balenoptera 
rostrata, shows that in the whalebone whales the muscles of each side sur- 
rounding the laryngeal pouch are attached by one extremity to the angle of the 
thyroid, and by the other to the body of the arytenoid and free border of the 
cricoid cartilage. In other words, we have in them a muscle which corresponds 
exactly to the thyro-arytenoid of other mammals, including the toothed whales. 
The cricoid attachment of the muscle appears to militate against this interpre- 
tation, but as neither TURNER nor CARTE and MACALISTER refer to a lateral 
crico-arytenoid, it seems by no means improbable that these cricoidal fibres 
may represent the crico-arytenoideus-lateralis. 
Now, if we imagine the laryngeal sac above described in Beluga to be ex- 
panded so as to project beyond the larynx opposite the interval between the 
cricoid and thyroid cartilages, accompanied by an adaptive alteration in the 
form of these cartilages, we should have the pouch invested by an almost com- 
plete layer of circular muscular fibres similar to that described by Sanp1irort,§ 
Escuricut and REINHARDT,|| TURNER, and CARTE and MACALISTER} in different 
species of whalebone whales. 
Taking then into consideration—1st, The essentially bilateral character of ; 
the laryngeal sac of the toothed whales ; 2d, The relation in which it stands to 
the thyroid cartilage and to the thyro-arytenoid muscles,—we come to the con- 
clusion that the relatively small pouches of the toothed whales are homologous 
with the ventricles of Morgagni of other mammals, and that the enormous — 
laryngeal sac of the whalebone whales must be equally regarded as their 
morphological equivalent. 
The comparative shortness and non-union apically of the epiglottidean 
and arytenoid cartilages has been already referred to as characteristic of the 
whalebone whales. A still more interesting modification of the arytenoid 
cartilages in that group appears to be consequent upon the condition of the 
* X. p. 129. + XVIL p. 238. t L p. 238, 
§ XXIV. p. 246. || XX. p. 101. q XVIL p. 238. 
