210 



ANATOMY OF VERTEBRATES. 



154 



Orycteropus (ib. p. 404) ; but the olfactory ones are far more 

 remarkable for both size and complexity. In the true Anteaters 

 (Myrmecophaga) the ethmoturbinals, though large, are less de- 

 veloped than in armadillos. The inferior turbinal is a long 

 slightly rolled up lamina. In sloths, as described in vol. ii. 

 p. 406, the olfactory chamber extends backward above the 

 rhinencephalic one into the frontal bone, and below it into the 

 sphenoid. The extension of air-sinuses therefrom is still greater 

 in the extinct megatherioids (ib. 407). 



The baleen-bearing whales are those of the Cetacea which 

 alone have olfactory nerves, although all possess the ' crura 

 rhinencephali.' The pituitary membrane supported by the tur- 

 binal bone is remarkable for the plexus of large vessels behind 

 it. The cetacean modifications of the nasal passages will be 

 described with the respiratory organs, to which they mainly 

 relate. 



In Sirenia the nostrils are subterminal, at the top of the obtuse 

 muzzle, and provided with movable gristles : the nasal passages 

 contain both ethmo- and maxillo-turbinals, the latter, like the 

 former, gristly ; the small almond-shaped bones wedged into the 



fore part of the frontals are, 

 as Cuvier held, nasals, not 

 turbinals. 1 The nasal passages 

 are short, narrow, sub vertical: 

 the ethmoturbinal is short and 

 longitudinally lamellate. The 

 olfactory nerves are fewer 

 and the cribriform plates 

 smaller in the Dugong than 

 in the Manatee. 



In the Elephant that part 

 of the nasal cavity, fig. 154, 

 which is appropriated to the 

 essential parts of the olfac- 

 tory organ is contracted and 

 narrow, and the passages, a, 

 b, are relatively short : they 

 are, however, much prolonged 

 by the accessory appendage, 

 called ' trunk,' at the extre- 

 mity of Avhich open the nos- 

 trils (vol. ii. p. 282, fig. 162, ?i), and are as much expanded 

 1 ' Cornets inferieurs,' De Bl. ; civ'. Gravigradc?, p. 39. 



Section of Elephant's skull, showing nasal passage. 



