Organ of Smell. 141 



Molility. 



The Rodentia offer the least, and the In-Enamellata the greatest 

 power of protrusion and mobility of the tongue in the whole Mam- 

 malian class. 



Structure^ 



Host Cetd offer a marked contrast to the other Mammalia in hav- 

 ing the skin of the tongue separated from the flesh by a layer of 

 blubber. 



Spines. 



In the Felid(B (Sectorialia), JPteropidcB (Cheiroptera), and especi- 

 ally in Ornithorhyncus (Monotremata), the anterior part of the 

 tongue is covered with hard horny spines. 



In the Bugong (Sirenia) a large but short thick retro verted horny 

 process projects from each side of the base of the tongue. 



C. Organ of Smell. 



The Olfactory organ of Mammalia is seldom absent ; it 

 differs from that of other Yertebrata both in the cribriform 

 lamina of the Ethmoid (of which the apertures transmit the 

 branches of the first pair of nerves to the nasal cavity) in 

 the sinuses, subsidiary cavities usually divided into mutually 

 communicating cells, which may exist in the frontal, sphenoid, 

 and superior maxillary bones ; and- in the great provision 

 made by bony and gristly laminae for the support of the 

 olfactory membranes. It is very exceptional to find this 

 organ wanting, but the extent of its development is very 

 variable, especially in the matter of the accessory cavities. 

 There is frequently* found, on each side of the cartilaginous 

 reptum of the nose, a longitudinal sac, surrounded by a car- 

 tilaginous sheath, and lined internally by a glandular mucous 

 membrane, which communicates with a duct running through 

 the foramina incisiva to the palate. Of the three turbinated 

 bones, the inferior is generally most developed. In animals 

 provided with a snout the nasal cartilages are lengthened 

 out into a tube, w^hich is covered with muscles that move it 



* Ruminantia and Rodentia. 



