LARYNX OF MAMMALIA. 589 



versed by the air-passage ] : and in the great Cachalot it is this 

 disproportionately enveloped f bony nostril ' which is described as 

 the ( single canal ' bv Hunter. 2 In the BalcRnidoR the two narial 



O ' 



canals are continued from the blow-holes ; distinct from one 

 another to the lower and hinder border of the bony septum. In 

 all Cetacea a dark pigment is continued with the dense epithelial 

 lining of the narial passages from the blow-hole down to the bony 

 tract. The phenomenon described and figured as the ' spouting of 

 the Whale ' consists chiefly of the expired pulmonary vapour : it 

 does not include water received into the pharynx from the mouth; 

 but it may contain that which has been diverted from the nasal 

 passage and accumulated in the sacculi : and the appearance of a 

 fountain may be enhanced by superincumbent sea-water i blown 

 up ' in the violent act of expiration, begun before the bljw-hole 

 itself had emerged. 



Similarity of structure can as little be predicated of the be- 

 ginning of the air-passage as of the digestive and circulating sys- 

 tems, in the herbivorous and the carnivorous marine apodal Mam- 

 mals. The Dugong and Dolphin present opposite extremes, e. g. 

 in the development of the epiglottis, which can hardly be said to 

 exist in Sirenia. 3 The glottis is very small and T-shaped, the 

 upper transverse slit being crescentic, with the horns bent a 

 little way outside the vertical slit: the epiglottis is not long enough 

 to close or cover this, but makes an obtuse prominence in front 

 of the glottis : the sides of the opening are formed by the mem- 

 brane covering the thin convex borders of the arvtenoids. The 



j / 



cartilaginous wings of the thyroid are not confluent, but are joined 

 anteriorly, for a short way, by sclerous tissue, and below this by 

 membrane and areolar tissue: the mesial cleft below is continued 

 on as a fissure to the upper cleft of the thyroid : each wing is an 

 irregular rhomboid, of which the foremost end is the point of 

 junction with its fellow, while the opposite angle is produced into 

 the f inferior cornu,' and is similarly connected by sclerous fibres 

 to a prominence on the side of the cricoid : the intermediate angle 

 on the posterior margin of the thyroid feebly represents the 

 ' superior cornu,' which is connected to the thyrohyal by ligament 

 including; a nuclear ' cartilage of Moro-ao-ni.' The cricoid is a 



^j CJ G C? 



larger cartilage, and forms a complete ring : its broad posterior 

 surface offers three longitudinal facets one medial, narrow but 

 expanding above and below, and two lateral and broad : the lower 

 border describes three straight lines : the upper border is very 

 thick, and presents, on each side, an elliptical convex articular 



1 xux'. p. 37, pi. 13, fig. 1, ol. - Ibid. 3 cxvn". p. 30 (1838). 



