230 CLASS XV. 



receives a disagreeable stimulus from certain objects. The tongue is 

 here principally of service as an instrument for seizing or swallowing 

 the food, or, as we have just said, as an organ of touch. In many 

 toads and frogs the tongue is membranous, smooth, covered with 

 mucus, attached in front and free behind, and when at rest thrown 

 back in the mouth, whilst in seizing the prey it is thrown over, and, 

 with the hinder part forward, is extended from the mouth. The 

 Pipa and the genus Xenopus have no tongue at all. In the sala- 

 manders the tongue is free at the edges alone. In most serpents it 

 is very smooth, and is divided at the apex into two flexible fila- 

 ments; its base is inclosed in a membranous sheath; the same 

 disposition is found in certain lizards. The prehensile tongue of 

 the chameleon is capable of great extension, and is knob-shaped 

 anteriorly. In most lacertine animals the tongue is elongate, trian- 

 gular, slightly notched in the middle at the apex, and but seldom, 

 as in Iguana, closely beset with fine papillae or villi, ordinarily only 

 wrinkled or covered with scales. The tongue in the crocodile is 

 membranous, attached at the point and sides to the bottom of the 

 oral cavity between the lateral pieces of the lower jaw, so that 

 formerly its presence was not recognised. Its hinder part is how- 

 ever capable of motion and can be elevated by the tongue-bone, so 

 that a fold or plait is formed which covers the entrance into the 

 ossophagus and prevents the water from entering it. Deglutition 

 therefore, by which this fold is again depressed, is not performed in 

 water but on dry land 1 . The tongue of the tortoises is thick and 

 membranous; in the turtles without papillse, but with many furrows 

 on the surface, in the land-tortoises covered with numerous very 

 thin flat villi thickly set. In the fresh-water tortoises some small 

 papillae alone are set on the fore part of the tongue, whilst elsewhere 

 it is free from them, though in some degree furrowed. In these last, 

 as in Iguana, taste is probably more fully developed than in other 

 reptiles. 



The cavity of the nose in reptiles has apertures opening into 

 the mouth or the gullet, a communication which prevails in all 

 vertebrate animals that breathe by lungs. The distance between 



1 A. DE HUMBOLDT Recutil d' Observations de Zoologie et d'Anat. Comp. Paris, 

 1811, i. p. 10, PL iv. No. x. OWEN Catal. of the Physiol. Series of Comp. Anat. of the 

 Roy. Coll. of Surgeons, n. London, 1834, p. 161, PI. xxvm. fig. i. 



