160 KEPTILIA. 



tor and retractor, and four to five additional pairs of muscles, a de- 

 tailed description of which would lead us out of the plan of the pres- 

 ent work. 



The study of the different structural conditions of the lingual 

 bone possesses a great amount of interest with the philosophical 

 or transcendental comparative anatomist, namely, in reference to 

 the development of the branchial apparatus, or of the visceral 

 arches, and the mode of division of the foetal vessels in the Verte- 

 brata. 



The tongue may in the Reptilia be frequently used as an im- 

 plement of touch. Special organs of touch do not exist, but in the 

 naked Amphibia, as the Frogs, the whole skin is endowed with the 

 highest sensibility, being supplied by numerous nervous filaments, 

 and it is on this account that, on irritating the skin in these animals, 

 they exhibit such strong and varied reflex movements, and are there- 

 by best adapted for making experiments upon the dynamics of the 

 nervous system. 



DIGESTIVE SYSTEM. 







THE form and armature of the jaws is exceedingly diversified in 

 the Reptilia. The Teeth, when present, never serve to masticate, 

 but only to seize the prey, or else they form, as in the Venomous 

 Serpents, what occurs in no other class of animals, peculiarly con- 

 structed weapons for inflicting a deadly wound. 



The teeth are completely wanting in the order Chelonia ; the 

 maxillae, with the exception of those of the Chelydes, which are 

 merely covered by skin, are invested with horn, consisting of super- 

 imposed lamellae, like those of Birds. In Trionyx, however, the lips 

 are soft and fleshy. 



Some edentulous genera are also found among the Batrachia, 

 e. g., Pipa. The Toads have palatal teeth, and besides these in 

 the Frogs, there are rows of short pointed teeth in the upper jaw, 

 and more rarely also in the lower jaw, as in the genus Hemifractus, 

 and the Tritons, and Salamanders. Similar diversities occur in 

 the Ichthyodea ; thus Proteus possesses teeth in both the upper and 

 lower jaws, and the Axolotl also upon the palate, while in Siren 

 a pair of large dental plates are found upon the palate, but no teeth 

 on the inter and supra maxillary bones. 



The Sauria, however, exhibit the greatest variety in this respect. 

 In some cases, numerous very small and pointed teeth stand prin- 



