VERTEBRATA : AMPHIBIA. 513 



rinthodonts possessed a ventral armour of bony scales. In- 

 tegumentary ossifications are also developed in some other 

 cases (e.g., Ceratophrys). 



As regards the digestive system of the Amphibia there is 

 little to say, except that the rectum opens, as it does in Rep- 

 tiles, into a common chamber or " cloaca," into which are also 

 discharged the secretions of the kidneys and generative organs. 

 A liver, gall-bladder, spleen, and pancreas are always present. 

 Singular pulsating cavities, belonging to the lymphatic system, 

 and known as "lymph-hearts," are also present in the higher 

 Amphibians. The alimentary canal is much longer in the lar-* 

 val Amphibians than in the adult. A tongue may or may not ; 

 be present, but there are no salivary glands. Teeth are, 

 usually developed in the vomer, praemaxillae, maxillae, and 

 mandible, and are generally disposed in the upper jaw in the 

 form of two concentric semicircles. In the larvae of the Frogs 

 and Toads the front of the maxillae and mandible are encased 

 in a horny beak. 



A urinary bladder is present, opening into the cloaca, and 

 there are well-developed kidneys. The ducts of the reproduc- 

 tive organs communicate with the urinary ducts. The ova are 

 usually impregnated outside the body ; but internal impregna- 

 tion occurs in some of the Urodela. 



CHAPTER LVIII. 



ORDERS OF AMPHIBIA. 



THE Amphibia are usually divided by modern writers into 

 four orders, the old order Lepidota, comprising the Mud Fishes, 

 being now placed at the head of the Fishes, under the name 

 of Dipnoi* Whilst there is a general agreement as to the 

 number and characters of the Amphibian orders, the names 

 employed to designate them are very various, and it really 

 matters little which are adopted. 



ORDER I. OPHIOMORPHA, Owen ( = Gymnophiona, Huxley ; 

 Apoda, Peromela, Ophidobatrachia) : Serpentiform or vermi- 

 form Amphibians, without limbs ; anus terminal ; skin mostly 

 with horny scales imbedded in it. Eyes rudimentary or absent. 



This is a small order, including only certain snake-like, 

 vermiform animals (fig. 278) which are found in various tropi- 

 cal countries, burrowing in marshy ground, something like 



2 K 



