628 THE VALVULAR ACTION OF THE LARYNX. 



I. The aglottic type, in which the laryngeal cavity is not 

 separated into two spaces by well-marked vocal cords. 



II. The simple glottic type, in which there are well-marked 

 vocal cords, but in which no false cords nor ventricles are 

 present. 



III. The composite type, in which the upper or anterior 

 portion of the larynx is furnished with a second pair of cords — 

 commonly termed false or superior cords — and which are sepa- 

 rated from the true cords by a distinct ventricle. 



IV. The cavernous type, in which the cavity of the larynx is 

 in communication with a sinus possessing accessory pouches, of 

 which the mouths are situated in the ventricles of the larynx, 

 or in other parts of this organ. 



In following this classification, the animals whose larynges 

 determine their serial position will be mentioned indiscrimi- 

 nately, and peculiarities of the glottis briefly expressed, whilst 

 reference to the author who is responsible for the statement 

 will be made in a footnote. 



Class I. — In the disciform mammals, where the larynx has not 

 the function of a vocal instrument, but only that of insuring 

 continuity of respiratory work during deglutition, and main- 

 taining free communication between the trachea and nasal cavi- 

 ties. This form of organisation is found in the Cetaceans. 



The Dugong has no ventricle. 



In the Dolphin* the glottis opens into the posterior nares, 

 and has a pyramidal form. It is patent only at its summit, 

 and leaves at either side a passage for food. The pyramidal 

 elevation is formed by the arytenoids and the epiglottis. Prob- 

 ably in these, and in the Cetaceans generally, there is no voice, 

 as no true means for its production are present. 



Marsupialia. — In the Kangaroof there is no false cord, no 

 ventricle, and only the faintest indication of true cords. The 

 arytenoids are capable of considerable elevation, and permit the 

 passage of air through a large gap between their inner surfaces. 



The Kangaroo has a cavernous sinus. 



It is probable that the Kangaroo is mute. 



The foetal Hippopotamus has no cords but a simple longi- 



• Cuvier, p. 797. t Milne-Edwards, p. 442. 



